Experienced this myself while playing Jailbreak with friends.
I tried to join their server but it was full. I thought the game was stuck but apparently the “Server full” text is now gone. While waiting for the blank screen I suddenly got a vague Connection Lost red error box. This pops up after only a couple minutes.
Trying to join that server again throws the error instantly.
You can try to wait it out or join a different server before trying again but you’ll be met with the same Connection Lost error.
The only solution is to have your friends leave the server and everybody finds a new one that they can hopefully all fit into.
Happens on PC/Mac. I don’t play enough to know when this issue started but I noticed it this weekend.