Bug/Issue Can go into friend's Co-Op file, but they can't go into mine!

We're both on the most current file as of today, and while I can connect to my friend's co-op game, everytime they try to join mine it just stays stuck at the "Connecting" screen. I haven't used up all my co-op slots on the file, and my other friend was able to come in with no issues.

Is there anything I can do to rectify this so they can play my co-op??