Can't play Custom Games

So I have this problem of not being able to play custom games. Whenever I try to join a custom game I get this message:

> CONNECTION FAILED
>
> Your connection to the game session has failed, please try again.

Every time I try to join a custom game I get this message. I can play matchmaking games without problems, but I cannot play custom games which are my favorite part. My NAT is OPEN. So that is not the problem. I have it set so that it automatically updates and when the game first came out I was able to play custom games without problems and only matchmaking was the problem. Now it’s the exact opposite. My NAT is a cone NAT but I don’t think that should matter. I have no idea what the problem is and if anyone does please say what it could possibly be. I desperately want to play custom games with my friends and I can’t so anything that you can provide would be fantastic.

Have you tried hard restarting your Xbox? It might be the “Marionberry” network issue, or it could be the joining friends bug that occurs when your Xbox goes into standby while Halo is running in the background. A hard restart will fix both of those issues. If a hard restart doesn’t fix your issue, then it might be something deeper.