Don't include old left rooms in /sync

synapse/handlers/sync.py

@@ -585,7 +585,8 @@ def incremental_sync_with_gap(self, sync_config, since_token):
                 sync_config, leave_event, since_token, tags_by_room,
                 account_data_by_room
             )
-            archived.append(room_sync)
+            if room_sync:
+                archived.append(room_sync)
 
         invited = [
             InvitedSyncResult(room_id=event.room_id, invite=event)
@@ -726,6 +727,9 @@ def incremental_sync_for_archived_room(self, sync_config, leave_event,
 
         leave_token = since_token.copy_and_replace("room_key", stream_token)
 
+        if since_token.is_after(leave_token):
+            defer.returnValue(None)
+
         batch = yield self.load_filtered_recents(
             leave_event.room_id, sync_config, leave_token, since_token,
         )