A very unfortunate bug shipped in 4.22 that causes a crash in many cases when a client is disconnected from the network, such as when unplugging the network cable. This will be a cert failure on consoles and could block shipping multiplayer games if a fix isn't applied.
The fix is in 4.23 but never made it in 4.22. We'd need to spot merge 5239735 and 5239743.
Many licensees have run into this problem and reported it on UDN, see for example:
From various reports on UDN, this can be reproduced by pulling the network cable while joining a server, or disabling the network adapter while joining a server.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-77189 in the post.