diff --git a/storage_controller/src/service.rs b/storage_controller/src/service.rs
index c0c5bc371a..222cb9fdd4 100644
--- a/storage_controller/src/service.rs
+++ b/storage_controller/src/service.rs
@@ -3572,6 +3572,11 @@ impl Service {
                 .iter()
                 .any(|i| i.generation.is_none() || i.generation_pageserver.is_none())
             {
+                let shard_generations = generations
+                    .into_iter()
+                    .map(|i| (i.tenant_shard_id, (i.generation, i.generation_pageserver)))
+                    .collect::<HashMap<_, _>>();
+
                 // One or more shards has not been attached to a pageserver.  Check if this is because it's configured
                 // to be detached (409: caller should give up), or because it's meant to be attached but isn't yet (503: caller should retry)
                 let locked = self.inner.read().unwrap();
@@ -3582,6 +3587,28 @@ impl Service {
                         PlacementPolicy::Attached(_) => {
                             // This shard is meant to be attached: the caller is not wrong to try and
                             // use this function, but we can't service the request right now.
+                            let Some(generation) = shard_generations.get(shard_id) else {
+                                // This can only happen if there is a split brain controller modifying the database.  This should
+                                // never happen when testing, and if it happens in production we can only log the issue.
+                                debug_assert!(false);
+                                tracing::error!("Shard {shard_id} not found in generation state!  Is another rogue controller running?");
+                                continue;
+                            };
+                            let (generation, generation_pageserver) = generation;
+                            if let Some(generation) = generation {
+                                if generation_pageserver.is_none() {
+                                    // This is legitimate only in a very narrow window where the shard was only just configured into
+                                    // Attached mode after being created in Secondary or Detached mode, and it has had its generation
+                                    // set but not yet had a Reconciler run (reconciler is the only thing that sets generation_pageserver).
+                                    tracing::warn!("Shard {shard_id} generation is set ({generation:?}) but generation_pageserver is None, reconciler not run yet?");
+                                }
+                            } else {
+                                // This should never happen: a shard with no generation is only permitted when it was created in some state
+                                // other than PlacementPolicy::Attached (and generation is always written to DB before setting Attached in memory)
+                                debug_assert!(false);
+                                tracing::error!("Shard {shard_id} generation is None, but it is in PlacementPolicy::Attached mode!");
+                                continue;
+                            }
                         }
                         PlacementPolicy::Secondary | PlacementPolicy::Detached => {
                             return Err(ApiError::Conflict(format!(