diff --git a/locales/rn/ar.json b/locales/rn/ar.json
index 28c4edad..99dea6b7 100644
--- a/locales/rn/ar.json
+++ b/locales/rn/ar.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, zero {يبدأ بعد # ساعة} one {يبدأ بعد ساعة واحدة} two {يبدأ بعد ساعتين} few {يبدأ بعد # ساعات} many {يبدأ بعد # ساعة} other {يبدأ بعد # ساعة}}",
       "starts_in_minutes": "{count, plural, zero {يبدأ بعد # دقيقة} one {يبدأ بعد دقيقة واحدة} two {يبدأ بعد دقيقتين} few {يبدأ بعد # دقائق} many {يبدأ بعد # دقيقة} other {يبدأ بعد # دقيقة}}"
     },
+    "occurrence_not_found_again": "لم يُحفظ التغيير: تعذّر العثور على هذا التكرار مرة أخرى على الخادم. حاول مرة أخرى.",
     "participants": {
       "limit_warning": "أكثر من {max, plural, zero {# مشارك} one {مشارك واحد} two {مشاركَين} few {# مشاركين} many {# مشاركًا} other {# مشارك}}، بمن فيهم المنظّم: قد يرفض الخادم حفظ هذا الحدث. يمكن للمسؤول رفع هذا الحد."
     },
diff --git a/locales/rn/ca.json b/locales/rn/ca.json
index 17c0ea7f..3d24323b 100644
--- a/locales/rn/ca.json
+++ b/locales/rn/ca.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Comença d'aquí a # hora} other {Comença d'aquí a # hores}}",
       "starts_in_minutes": "{count, plural, one {Comença d'aquí a # minut} other {Comença d'aquí a # minuts}}"
     },
+    "occurrence_not_found_again": "No s'ha desat el canvi: no s'ha pogut tornar a trobar la repetició al servidor. Torneu-ho a provar.",
     "participants": {
       "limit_warning": "Més de {max, plural, one {# participant} other {# participants}}, inclòs l'organitzador: és possible que el servidor es negui a desar aquest esdeveniment. Un administrador pot augmentar el límit."
     },
diff --git a/locales/rn/cs.json b/locales/rn/cs.json
index fabb1101..236db453 100644
--- a/locales/rn/cs.json
+++ b/locales/rn/cs.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Začíná za # hodinu} few {Začíná za # hodiny} many {Začíná za # hodiny} other {Začíná za # hodin}}",
       "starts_in_minutes": "{count, plural, one {Začíná za # minutu} few {Začíná za # minuty} many {Začíná za # minuty} other {Začíná za # minut}}"
     },
+    "occurrence_not_found_again": "Změna nebyla uložena: opakování se na serveru nepodařilo znovu najít. Zkuste to znovu.",
     "participants": {
       "limit_warning": "Více než {max, plural, one {# účastník} few {# účastníci} many {# účastníka} other {# účastníků}} včetně organizátora: server může uložení této události odmítnout. Správce může limit zvýšit."
     },
diff --git a/locales/rn/da.json b/locales/rn/da.json
index bd9dae7c..3e2d3245 100644
--- a/locales/rn/da.json
+++ b/locales/rn/da.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Starter om # time} other {Starter om # timer}}",
       "starts_in_minutes": "{count, plural, one {Starter om # minut} other {Starter om # minutter}}"
     },
+    "occurrence_not_found_again": "Ændringen blev ikke gemt: forekomsten kunne ikke findes igen på serveren. Prøv igen.",
     "participants": {
       "limit_warning": "Mere end {max, plural, one {# deltager} other {# deltagere}}, arrangøren medregnet: serveren kan afvise at gemme denne begivenhed. En administrator kan hæve grænsen."
     },
diff --git a/locales/rn/de.json b/locales/rn/de.json
index 3b0b76ac..500d7c1b 100644
--- a/locales/rn/de.json
+++ b/locales/rn/de.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Beginnt in # Stunde} other {Beginnt in # Stunden}}",
       "starts_in_minutes": "{count, plural, one {Beginnt in # Minute} other {Beginnt in # Minuten}}"
     },
+    "occurrence_not_found_again": "Die Änderung wurde nicht gespeichert: Der Termin konnte auf dem Server nicht wiedergefunden werden. Versuchen Sie es erneut.",
     "participants": {
       "limit_warning": "Mehr als {max, plural, one {# Teilnehmer} other {# Teilnehmer}}, den Organisator mitgezählt: Der Server lehnt das Speichern dieses Termins möglicherweise ab. Ihr Administrator kann das Limit erhöhen."
     },
diff --git a/locales/rn/en.json b/locales/rn/en.json
index f300ba16..5780c8cb 100644
--- a/locales/rn/en.json
+++ b/locales/rn/en.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Starts in # hour} other {Starts in # hours}}",
       "starts_in_minutes": "{count, plural, one {Starts in # minute} other {Starts in # minutes}}"
     },
+    "occurrence_not_found_again": "The change was not saved: the occurrence could not be found again on the server. Please try again.",
     "participants": {
       "limit_warning": "More than {max, plural, one {# participant} other {# participants}}, including the organizer: the server may refuse to save this event. An administrator can raise the limit."
     },
diff --git a/locales/rn/es.json b/locales/rn/es.json
index d9322700..ec8bdc77 100644
--- a/locales/rn/es.json
+++ b/locales/rn/es.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Comienza en # hora} other {Comienza en # horas}}",
       "starts_in_minutes": "{count, plural, one {Comienza en # minuto} other {Comienza en # minutos}}"
     },
+    "occurrence_not_found_again": "No se guardó el cambio: no se pudo volver a encontrar la repetición en el servidor. Inténtalo de nuevo.",
     "participants": {
       "limit_warning": "Más de {max, plural, one {# participante} other {# participantes}}, incluido el organizador: es posible que el servidor se niegue a guardar este evento. Un administrador puede aumentar el límite."
     },
diff --git a/locales/rn/fa.json b/locales/rn/fa.json
index 6d2daac1..1aad1dd1 100644
--- a/locales/rn/fa.json
+++ b/locales/rn/fa.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {# ساعت دیگر شروع می‌شود} other {# ساعت دیگر شروع می‌شود}}",
       "starts_in_minutes": "{count, plural, one {# دقیقه دیگر شروع می‌شود} other {# دقیقه دیگر شروع می‌شود}}"
     },
+    "occurrence_not_found_again": "تغییر ذخیره نشد: این تکرار دوباره روی سرور پیدا نشد. دوباره تلاش کنید.",
     "participants": {
       "limit_warning": "بیش از {max, plural, one {# شرکت‌کننده} other {# شرکت‌کننده}}، با احتساب برگزارکننده: ممکن است سرور ذخیره این رویداد را رد کند. مدیر سیستم می‌تواند این محدودیت را افزایش دهد."
     },
diff --git a/locales/rn/fr.json b/locales/rn/fr.json
index 92219edc..c56cb996 100644
--- a/locales/rn/fr.json
+++ b/locales/rn/fr.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Commence dans # heure} other {Commence dans # heures}}",
       "starts_in_minutes": "{count, plural, one {Commence dans # minute} other {Commence dans # minutes}}"
     },
+    "occurrence_not_found_again": "La modification n'a pas été enregistrée : l'occurrence n'a pas pu être retrouvée sur le serveur. Réessayez.",
     "participants": {
       "limit_warning": "Plus de {max, plural, one {# participant} other {# participants}}, organisateur compris : le serveur risque de refuser d'enregistrer cet événement. Un administrateur peut relever la limite."
     },
diff --git a/locales/rn/he.json b/locales/rn/he.json
index ffaea5ae..2f13e310 100644
--- a/locales/rn/he.json
+++ b/locales/rn/he.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {מתחיל בעוד שעה} two {מתחיל בעוד שעתיים} other {מתחיל בעוד # שעות}}",
       "starts_in_minutes": "{count, plural, one {מתחיל בעוד דקה} two {מתחיל בעוד שתי דקות} other {מתחיל בעוד # דקות}}"
     },
+    "occurrence_not_found_again": "השינוי לא נשמר: לא ניתן היה למצוא שוב את המופע בשרת. נסה שוב.",
     "participants": {
       "limit_warning": "יותר מ-{max, plural, one {# משתתף} other {# משתתפים}}, כולל המארגן: ייתכן שהשרת יסרב לשמור את האירוע. מנהל המערכת יכול להגדיל את המגבלה."
     },
diff --git a/locales/rn/hu.json b/locales/rn/hu.json
index eb6c5424..14f3e78f 100644
--- a/locales/rn/hu.json
+++ b/locales/rn/hu.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {# óra múlva kezdődik} other {# óra múlva kezdődik}}",
       "starts_in_minutes": "{count, plural, one {# perc múlva kezdődik} other {# perc múlva kezdődik}}"
     },
+    "occurrence_not_found_again": "A módosítás nem lett mentve: az alkalmat nem sikerült újra megtalálni a szerveren. Próbáld újra.",
     "participants": {
       "limit_warning": "Több mint {max, plural, one {# résztvevő} other {# résztvevő}}, a szervezőt is beleértve: a szerver elutasíthatja az esemény mentését. A rendszergazda megemelheti a korlátot."
     },
diff --git a/locales/rn/it.json b/locales/rn/it.json
index ea71283a..fdfe18d1 100644
--- a/locales/rn/it.json
+++ b/locales/rn/it.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Inizia tra # ora} other {Inizia tra # ore}}",
       "starts_in_minutes": "{count, plural, one {Inizia tra # minuto} other {Inizia tra # minuti}}"
     },
+    "occurrence_not_found_again": "La modifica non è stata salvata: non è stato possibile ritrovare l'occorrenza sul server. Riprova.",
     "participants": {
       "limit_warning": "Più di {max, plural, one {# partecipante} other {# partecipanti}}, organizzatore incluso: il server potrebbe rifiutarsi di salvare questo evento. Un amministratore può aumentare il limite."
     },
diff --git a/locales/rn/ja.json b/locales/rn/ja.json
index 4417adb8..3f196e5e 100644
--- a/locales/rn/ja.json
+++ b/locales/rn/ja.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, other {#時間後に開始}}",
       "starts_in_minutes": "{count, plural, other {#分後に開始}}"
     },
+    "occurrence_not_found_again": "変更は保存されませんでした：サーバーで対象の回をもう一度見つけられませんでした。もう一度お試しください。",
     "participants": {
       "limit_warning": "参加者が主催者を含めて{max, plural, other {#人}}を超えています。サーバーがこの予定の保存を拒否する可能性があります。管理者が上限を引き上げることができます。"
     },
diff --git a/locales/rn/ko.json b/locales/rn/ko.json
index 395ceb3e..36889ce5 100644
--- a/locales/rn/ko.json
+++ b/locales/rn/ko.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, other {#시간 후 시작}}",
       "starts_in_minutes": "{count, plural, other {#분 후 시작}}"
     },
+    "occurrence_not_found_again": "변경 사항이 저장되지 않았어요. 서버에서 해당 회차를 다시 찾을 수 없었어요. 다시 시도해 주세요.",
     "participants": {
       "limit_warning": "참석자가 주최자를 포함해 {max, plural, other {#명}}을 넘어요. 서버가 이 일정의 저장을 거부할 수 있어요. 관리자가 한도를 늘릴 수 있어요."
     },
diff --git a/locales/rn/lv.json b/locales/rn/lv.json
index 5500acbb..ba42cfa0 100644
--- a/locales/rn/lv.json
+++ b/locales/rn/lv.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, zero {Sākas pēc # stundām} one {Sākas pēc # stundas} other {Sākas pēc # stundām}}",
       "starts_in_minutes": "{count, plural, zero {Sākas pēc # minūtēm} one {Sākas pēc # minūtes} other {Sākas pēc # minūtēm}}"
     },
+    "occurrence_not_found_again": "Izmaiņas netika saglabātas: šo notikuma reizi serverī neizdevās atrast vēlreiz. Mēģiniet vēlreiz.",
     "participants": {
       "limit_warning": "Vairāk nekā {max, plural, one {# dalībnieks} other {# dalībnieki}}, ieskaitot organizatoru: serveris var atteikties saglabāt šo pasākumu. Administrators var palielināt ierobežojumu."
     },
diff --git a/locales/rn/mn.json b/locales/rn/mn.json
index fbb0a1be..1861448f 100644
--- a/locales/rn/mn.json
+++ b/locales/rn/mn.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {# цагийн дараа эхэлнэ} other {# цагийн дараа эхэлнэ}}",
       "starts_in_minutes": "{count, plural, one {# минутын дараа эхэлнэ} other {# минутын дараа эхэлнэ}}"
     },
+    "occurrence_not_found_again": "Өөрчлөлт хадгалагдсангүй: энэ удаагийн үйл явдлыг серверээс дахин олж чадсангүй. Дахин оролдоно уу.",
     "participants": {
       "limit_warning": "Зохион байгуулагчийг оролцуулаад {max, plural, other {#}}-аас олон оролцогч: сервер энэ үйл явдлыг хадгалахаас татгалзаж магадгүй. Администратор хязгаарыг нэмэгдүүлэх боломжтой."
     },
diff --git a/locales/rn/nb.json b/locales/rn/nb.json
index b15c2314..537a5920 100644
--- a/locales/rn/nb.json
+++ b/locales/rn/nb.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Starter om # time} other {Starter om # timer}}",
       "starts_in_minutes": "{count, plural, one {Starter om # minutt} other {Starter om # minutter}}"
     },
+    "occurrence_not_found_again": "Endringen ble ikke lagret: forekomsten ble ikke funnet igjen på serveren. Prøv igjen.",
     "participants": {
       "limit_warning": "Mer enn {max, plural, one {# deltaker} other {# deltakere}}, arrangøren medregnet: serveren kan nekte å lagre denne hendelsen. En administrator kan øke grensen."
     },
diff --git a/locales/rn/nl.json b/locales/rn/nl.json
index 1d1bf74c..a5709895 100644
--- a/locales/rn/nl.json
+++ b/locales/rn/nl.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Begint over # uur} other {Begint over # uur}}",
       "starts_in_minutes": "{count, plural, one {Begint over # minuut} other {Begint over # minuten}}"
     },
+    "occurrence_not_found_again": "De wijziging is niet opgeslagen: de herhaling kon niet opnieuw op de server worden gevonden. Probeer het opnieuw.",
     "participants": {
       "limit_warning": "Meer dan {max, plural, one {# deelnemer} other {# deelnemers}}, de organisator meegeteld: de server kan weigeren dit evenement op te slaan. Een beheerder kan de limiet verhogen."
     },
diff --git a/locales/rn/pl.json b/locales/rn/pl.json
index e7ee4eb6..95028881 100644
--- a/locales/rn/pl.json
+++ b/locales/rn/pl.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Zaczyna się za # godzinę} few {Zaczyna się za # godziny} many {Zaczyna się za # godzin} other {Zaczyna się za # godziny}}",
       "starts_in_minutes": "{count, plural, one {Zaczyna się za # minutę} few {Zaczyna się za # minuty} many {Zaczyna się za # minut} other {Zaczyna się za # minuty}}"
     },
+    "occurrence_not_found_again": "Zmiana nie została zapisana: nie udało się ponownie znaleźć wystąpienia na serwerze. Spróbuj ponownie.",
     "participants": {
       "limit_warning": "Ponad {max, plural, one {# uczestnika} few {# uczestników} many {# uczestników} other {# uczestnika}} łącznie z organizatorem: serwer może odmówić zapisania tego wydarzenia. Administrator może zwiększyć limit."
     },
diff --git a/locales/rn/pt.json b/locales/rn/pt.json
index 31461840..aeb505b0 100644
--- a/locales/rn/pt.json
+++ b/locales/rn/pt.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Começa em # hora} other {Começa em # horas}}",
       "starts_in_minutes": "{count, plural, one {Começa em # minuto} other {Começa em # minutos}}"
     },
+    "occurrence_not_found_again": "A alteração não foi salva: não foi possível encontrar a repetição novamente no servidor. Tente novamente.",
     "participants": {
       "limit_warning": "Mais de {max, plural, one {# participante} other {# participantes}}, incluindo o organizador: o servidor pode se recusar a salvar este evento. Um administrador pode aumentar o limite."
     },
diff --git a/locales/rn/ro.json b/locales/rn/ro.json
index 0442289c..7ed75778 100644
--- a/locales/rn/ro.json
+++ b/locales/rn/ro.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Începe peste # oră} few {Începe peste # ore} other {Începe peste # de ore}}",
       "starts_in_minutes": "{count, plural, one {Începe peste # minut} few {Începe peste # minute} other {Începe peste # de minute}}"
     },
+    "occurrence_not_found_again": "Modificarea nu a fost salvată: ocurența nu a mai putut fi găsită pe server. Încercați din nou.",
     "participants": {
       "limit_warning": "Mai mult de {max, plural, one {# participant} few {# participanți} other {# de participanți}}, inclusiv organizatorul: serverul poate refuza salvarea acestui eveniment. Un administrator poate mări limita."
     },
diff --git a/locales/rn/ru.json b/locales/rn/ru.json
index d2e4a783..6c282026 100644
--- a/locales/rn/ru.json
+++ b/locales/rn/ru.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Начнётся через # час} few {Начнётся через # часа} many {Начнётся через # часов} other {Начнётся через # часа}}",
       "starts_in_minutes": "{count, plural, one {Начнётся через # минуту} few {Начнётся через # минуты} many {Начнётся через # минут} other {Начнётся через # минуты}}"
     },
+    "occurrence_not_found_again": "Изменение не сохранено: не удалось снова найти это повторение на сервере. Попробуйте ещё раз.",
     "participants": {
       "limit_warning": "Больше {max, plural, one {# участника} few {# участников} many {# участников} other {# участника}}, включая организатора: сервер может отказаться сохранить это событие. Администратор может увеличить лимит."
     },
diff --git a/locales/rn/sk.json b/locales/rn/sk.json
index f2cf7c93..f8041e38 100644
--- a/locales/rn/sk.json
+++ b/locales/rn/sk.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Začína o # hodinu} few {Začína o # hodiny} many {Začína o # hodiny} other {Začína o # hodín}}",
       "starts_in_minutes": "{count, plural, one {Začína o # minútu} few {Začína o # minúty} many {Začína o # minúty} other {Začína o # minút}}"
     },
+    "occurrence_not_found_again": "Zmena sa neuložila: opakovanie sa na serveri nepodarilo znova nájsť. Skúste to znova.",
     "participants": {
       "limit_warning": "Viac ako {max, plural, one {# účastník} few {# účastníci} many {# účastníka} other {# účastníkov}} vrátane organizátora: server môže odmietnuť uloženie tejto udalosti. Správca môže limit zvýšiť."
     },
diff --git a/locales/rn/tr.json b/locales/rn/tr.json
index dd9e86b4..f642523b 100644
--- a/locales/rn/tr.json
+++ b/locales/rn/tr.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {# saat sonra başlıyor} other {# saat sonra başlıyor}}",
       "starts_in_minutes": "{count, plural, one {# dakika sonra başlıyor} other {# dakika sonra başlıyor}}"
     },
+    "occurrence_not_found_again": "Değişiklik kaydedilmedi: bu tekrar sunucuda yeniden bulunamadı. Tekrar deneyin.",
     "participants": {
       "limit_warning": "Organizatör dahil {max, plural, one {# katılımcıdan} other {# katılımcıdan}} fazla: sunucu bu etkinliği kaydetmeyi reddedebilir. Bir yönetici bu sınırı yükseltebilir."
     },
diff --git a/locales/rn/uk.json b/locales/rn/uk.json
index 5e57c30b..db20f423 100644
--- a/locales/rn/uk.json
+++ b/locales/rn/uk.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, one {Почнеться через # годину} few {Почнеться через # години} many {Почнеться через # годин} other {Почнеться через # години}}",
       "starts_in_minutes": "{count, plural, one {Почнеться через # хвилину} few {Почнеться через # хвилини} many {Почнеться через # хвилин} other {Почнеться через # хвилини}}"
     },
+    "occurrence_not_found_again": "Зміну не збережено: не вдалося знову знайти це повторення на сервері. Спробуйте ще раз.",
     "participants": {
       "limit_warning": "Понад {max, plural, one {# учасника} few {# учасників} many {# учасників} other {# учасника}}, включно з організатором: сервер може відмовитися зберегти цю подію. Адміністратор може збільшити ліміт."
     },
diff --git a/locales/rn/zh-TW.json b/locales/rn/zh-TW.json
index b925d494..ad3ec004 100644
--- a/locales/rn/zh-TW.json
+++ b/locales/rn/zh-TW.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, other {# 小時後開始}}",
       "starts_in_minutes": "{count, plural, other {# 分鐘後開始}}"
     },
+    "occurrence_not_found_again": "變更未儲存：無法在伺服器上再次找到這一次的活動。請再試一次。",
     "participants": {
       "limit_warning": "參與者（含主辦人）超過 {max, plural, other {# 位}}：伺服器可能會拒絕儲存此活動。管理員可以提高此限制。"
     },
diff --git a/locales/rn/zh.json b/locales/rn/zh.json
index 1956245e..4df00eaa 100644
--- a/locales/rn/zh.json
+++ b/locales/rn/zh.json
@@ -84,6 +84,7 @@
       "starts_in_hours": "{count, plural, other {# 小时后开始}}",
       "starts_in_minutes": "{count, plural, other {# 分钟后开始}}"
     },
+    "occurrence_not_found_again": "更改未保存：无法在服务器上再次找到这一次的活动。请重试。",
     "participants": {
       "limit_warning": "参与者（含组织者）超过 {max, plural, other {# 位}}：服务器可能会拒绝保存此活动。管理员可以提高此限制。"
     },
diff --git a/src/stores/__tests__/calendar-store-occurrence-answers.test.ts b/src/stores/__tests__/calendar-store-occurrence-answers.test.ts
index a5f0c40a..529fc654 100644
--- a/src/stores/__tests__/calendar-store-occurrence-answers.test.ts
+++ b/src/stores/__tests__/calendar-store-occurrence-answers.test.ts
@@ -92,7 +92,8 @@ beforeEach(() => {
 describe.each(['0.16.23', '1.0'])('a first change to one server occurrence on Stalwart %s', () => {
   it('writes the override as it stands, then sends the change to its re-read id', async () => {
     useCalendarStore.setState({ events: [serverOccurrence()] });
-    // The new override gives the occurrence another synthetic id.
+    // The new override gives the occurrence another synthetic id (positional
+    // ids, up to 0.16.20; 0.16.21 and 1.0 keep it, see below).
     mockQueryExpanded.mockResolvedValue(['s9', 'other']);
     mockGetEvents.mockImplementation(async (ids: string[]) => (ids.includes('s9')
       ? [
@@ -113,6 +114,18 @@ describe.each(['0.16.23', '1.0'])('a first change to one server occurrence on St
     expect(mockGetEvents).toHaveBeenCalledWith(['s9', 'other'], undefined, { expanded: true });
   });
 
+  it('sends the change to the same id when the override keeps it (recurrence-keyed ids, live)', async () => {
+    useCalendarStore.setState({ events: [serverOccurrence()] });
+    mockQueryExpanded.mockResolvedValue(['s1']);
+    mockGetEvents.mockResolvedValue([{ id: 's1', baseEventId: 'base', recurrenceId: RID, start: RID, duration: 'PT1H' } as CalendarEvent]);
+
+    await useCalendarStore.getState().updateEvent('s1', { title: 'Standup, room 2', participants } as Partial<CalendarEvent>, {
+      sendSchedulingMessages: true,
+    });
+
+    expect(mockUpdate.mock.calls.map(([id, , schedule]) => [id, schedule])).toEqual([['s1', false], ['s1', true]]);
+  });
+
   it('sends the change once when it asks the attendees again (a move)', async () => {
     useCalendarStore.setState({ events: [serverOccurrence()] });
 
@@ -142,15 +155,40 @@ describe.each(['0.16.23', '1.0'])('a first change to one server occurrence on St
     expect(mockUpdate.mock.calls.map(([id, , schedule]) => [id, schedule])).toEqual([['s1', false]]);
   });
 
-  it('sends the change to the old id when the occurrence cannot be found again', async () => {
+  // Up to 0.16.20 Stalwart's synthetic ids are positions in the series'
+  // expansion (calendar_event/mod.rs): after the new override "s1" can name
+  // the next occurrence, which must not get the change and its scheduling
+  // messages. 0.16.21 and 1.0 keep the id; the lookup finds it again there.
+  it.each([
+    ['is not listed', () => mockQueryExpanded.mockResolvedValue(null)],
+    ['cannot be read', () => mockQueryExpanded.mockRejectedValue(new Error('Network request failed'))],
+    ['is listed twice', () => {
+      mockQueryExpanded.mockResolvedValue(['s9', 's10']);
+      mockGetEvents.mockResolvedValue([
+        { id: 's9', baseEventId: 'base', recurrenceId: RID, start: RID } as CalendarEvent,
+        { id: 's10', baseEventId: 'base', recurrenceId: RID, start: RID } as CalendarEvent,
+      ]);
+    }],
+  ])('sends nothing more, and says so, when the occurrence %s after its quiet override', async (_what, arrange) => {
     useCalendarStore.setState({ events: [serverOccurrence()] });
-    mockQueryExpanded.mockResolvedValue(null);
+    arrange();
+    const refresh = vi.fn(async () => undefined);
+    const { refresh: storeRefresh } = useCalendarStore.getState();
+    useCalendarStore.setState({ refresh });
 
-    await useCalendarStore.getState().updateEvent('s1', { title: 'Standup, room 2', participants } as Partial<CalendarEvent>, {
-      sendSchedulingMessages: true,
-    });
+    try {
+      await expect(useCalendarStore.getState().updateEvent('s1', { title: 'Standup, room 2', participants } as Partial<CalendarEvent>, {
+        sendSchedulingMessages: true,
+      })).rejects.toThrow('The change was not saved: the occurrence could not be found again on the server. Please try again.');
+    } finally {
+      useCalendarStore.setState({ refresh: storeRefresh });
+    }
 
-    expect(mockUpdate.mock.calls.map(([id, , schedule]) => [id, schedule])).toEqual([['s1', false], ['s1', true]]);
+    // Only the override as the occurrence stands, which reaches no one.
+    expect(mockUpdate.mock.calls.map(([id, , schedule]) => [id, schedule])).toEqual([['s1', false]]);
+    // The ids in view may name other occurrences now: read them again.
+    expect(refresh).toHaveBeenCalled();
+    expect(useCalendarStore.getState().events[0].title).toBe('Standup');
   });
 });
 
diff --git a/src/stores/calendar-store.ts b/src/stores/calendar-store.ts
index c1c88ad0..515b6074 100644
--- a/src/stores/calendar-store.ts
+++ b/src/stores/calendar-store.ts
@@ -519,7 +519,8 @@ async function updateOccurrence(
 
 /**
  * The server occurrence of `instance`'s series at the same recurrence id, read
- * again: a new override can give an occurrence another synthetic id.
+ * again: a new override can give an occurrence another synthetic id. Null
+ * when the series lists none there, or more than one.
  */
 async function findServerOccurrence(
   instance: CalendarEvent,
@@ -531,7 +532,24 @@ async function findServerOccurrence(
   const ids = await queryExpandedEvents(new Date(at - DAY_MS).toISOString(), new Date(at + DAY_MS).toISOString(), accountId);
   if (!ids?.length) return null;
   const found = await fetchEvents(ids, accountId, { expanded: true });
-  return found.find((e) => e.baseEventId === instance.baseEventId && e.recurrenceId === instance.recurrenceId) ?? null;
+  const matches = found.filter((e) => e.baseEventId === instance.baseEventId && e.recurrenceId === instance.recurrenceId);
+  return matches.length === 1 ? matches[0] : null;
+}
+
+/**
+ * A first change to one occurrence could not be sent: after its quiet
+ * override was written, the occurrence was not found again (see
+ * updateOccurrenceInTwoSteps). That override changes nothing that shows, and
+ * a retry updates it, which reaches every attendee.
+ */
+export class OccurrenceNotFoundAgainError extends Error {
+  constructor() {
+    super(t(
+      'calendar.occurrence_not_found_again',
+      'The change was not saved: the occurrence could not be found again on the server. Please try again.',
+    ));
+    this.name = 'OccurrenceNotFoundAgainError';
+  }
 }
 
 /**
@@ -541,7 +559,12 @@ async function findServerOccurrence(
  * change; an update of an existing override reaches everyone. So the override
  * is written first as the occurrence stands, without scheduling, and the
  * change then goes out as an update of it. The occurrence is looked up again
- * in between: the new override can give it another synthetic id.
+ * in between: the new override can give it another synthetic id. When that
+ * fails, the change is not sent to the old id: up to 0.16.20 Stalwart's
+ * synthetic ids are positions in the series' expansion (calendar_event/
+ * mod.rs), and after the new override the old one can name the next
+ * occurrence, which would get the change and its scheduling messages.
+ * 0.16.21 and 1.0 key them by recurrence id, and the id stays (live).
  */
 async function updateOccurrenceInTwoSteps(
   instance: CalendarEvent,
@@ -552,7 +575,8 @@ async function updateOccurrenceInTwoSteps(
 ): Promise<void> {
   await updateOccurrence(instance, syntheticId, (options) => withNewOverrideDetails(instance, {}, options), false, accountId);
   const current = await findServerOccurrence(instance, accountId).catch(() => null);
-  await updateOccurrence(current ?? instance, current?.id ?? syntheticId, () => patch, sendSchedulingMessages, accountId);
+  if (!current) throw new OccurrenceNotFoundAgainError();
+  await updateOccurrence(current, current.id, () => patch, sendSchedulingMessages, accountId);
 }
 
 /**
@@ -945,7 +969,14 @@ export const useCalendarStore = create<CalendarState>()(
         await stopSeriesDefaultAlerts(storeEvent.baseEventId, accountId);
       }
       if (twoSteps) {
-        await updateOccurrenceInTwoSteps(storeEvent, realId, patch as Partial<CalendarEvent>, schedule, accountId);
+        try {
+          await updateOccurrenceInTwoSteps(storeEvent, realId, patch as Partial<CalendarEvent>, schedule, accountId);
+        } catch (err) {
+          // Its quiet override is on the server, and the series' occurrences
+          // may have other ids now: a retry must not go to the ones in view.
+          if (err instanceof OccurrenceNotFoundAgainError) await get().refresh().catch(() => undefined);
+          throw err;
+        }
       } else {
         await updateOccurrence(
           storeEvent,