Add some debugging to narrow down what is going on

synapse/handlers/room_member.py

@@ -452,6 +452,9 @@ class RoomMemberHandler(object):
                     )
 
         is_host_in_room = yield self._is_host_in_room(current_state_ids)
+        logger.info("Is host in room? %s" % is_host_in_room)
+        logger.info("effective_membership_state %s" % effective_membership_state)
+        logger.info("remote_room_hosts %s" % remote_room_hosts)
 
         if effective_membership_state == Membership.JOIN:
             if requester.is_guest:

synapse/handlers/sync.py

@@ -1386,6 +1386,7 @@ class SyncHandler(object):
 
         mem_change_events_by_room_id = {}
         for event in rooms_changed:
+            logger.warn("Membership %s" % event.room_id)
             mem_change_events_by_room_id.setdefault(event.room_id, []).append(event)
 
         newly_joined_rooms = []