even more debugging. Perhaps the issue is in the join event?

synapse/handlers/message.py

@@ -495,12 +495,14 @@ class EventCreationHandler(object):
                 try:
                     if "displayname" not in content:
                         content["displayname"] = yield profile.get_displayname(target)
+                        logger.info("Adding displayname to membership event")
                     if "avatar_url" not in content:
                         content["avatar_url"] = yield profile.get_avatar_url(target)
                 except Exception as e:
                     logger.info(
                         "Failed to get profile information for %r: %s", target, e
                     )
+                logger.info("Membership event content: %s", content)
 
         is_exempt = yield self._is_exempt_from_privacy_policy(builder, requester)
         if require_consent and not is_exempt:

synapse/state/__init__.py

@@ -136,6 +136,8 @@ class StateHandler(object):
         ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         state = ret.state
 
+        logger.info("state at %s: %s", latest_event_ids, state)
+
         if event_type:
             event_id = state.get((event_type, state_key))
             event = None
@@ -381,6 +383,8 @@ class StateHandler(object):
             room_id, event_ids
         )
 
+        logger.info("state groups at %s: %s", event_ids, state_groups_ids)
+
         if len(state_groups_ids) == 0:
             return _StateCacheEntry(state={}, state_group=None)
         elif len(state_groups_ids) == 1: