Check the retransmit rooms are _still_ full stated

synapse/handlers/sync.py

@@ -1380,24 +1380,30 @@ async def generate_sync_result(
 
         # Tweak the set of rooms to return to the client for eager (non-lazy) syncs.
         mutable_rooms_to_exclude = set(self.rooms_to_exclude_globally)
-        retransmit_room_ids = set()
         if not sync_config.filter_collection.lazy_load_members():
             # Non-lazy syncs should never include partially stated rooms.
             # Exclude all partially stated rooms from this sync.
             for room_id in mutable_joined_room_ids:
                 if await self.store.is_partial_state_room(room_id):
                     mutable_rooms_to_exclude.add(room_id)
 
-            # Incremental syncs should include rooms that became fully-stated during
-            # the sync period.
-            if since_token:
-                retransmit_room_ids.update(
-                    await self.store.get_un_partial_stated_rooms_between(
-                        since_token.un_partial_stated_rooms_key,
-                        now_token.un_partial_stated_rooms_key,
-                        mutable_joined_room_ids,
-                    )
+        # Incremental eager syncs should additionally include rooms that
+        # - we are joined to
+        # - are full-stated
+        # - became fully-stated at some point during the sync period
+        # (These rooms will have been omitted during a previous eager sync.)
+        retransmit_room_ids = set()
+        if since_token and not sync_config.filter_collection.lazy_load_members():
+            un_partial_stated_rooms = (
+                await self.store.get_un_partial_stated_rooms_between(
+                    since_token.un_partial_stated_rooms_key,
+                    now_token.un_partial_stated_rooms_key,
+                    mutable_joined_room_ids,
                 )
+            )
+            for room_id in un_partial_stated_rooms:
+                if not await self.store.is_partial_state_room(room_id):
+                    retransmit_room_ids.add(room_id)
 
         # Now we have our list of joined room IDs, exclude as configured and freeze
         joined_room_ids = frozenset(