xoros
I'm not sure, in "real time" case, it might have bug at server or client code. It's hard to reproduce the situation. Sorry I could not help you. (This is used queue to sync function, you are right.)
The server is wrote by myself and it might be not stable (buggy) at some corner case.
I might try to use pomelo game server to replace current server. But I'm not sure it could be used at Heroku.