Maybe the keepalive defaults got changed? All past references to the issue refer to some sort of keepalive to avoid the issue. For example [1] Be aware that some suggestions on [1] configure the sever, while your issue is on the client side (at least that is where the upgrade happened. You could also run your failing ssh connection with debug enabled, sometimes a message helps to identify the issue $ ssh -vvv x.x.x.x You could check if the defaults changed by comparing your old and new setup with -G like: $ ssh -G x.x.x.x That will report the configs used. I compared 18.10 and 19.04 and found those: $ diff ssh.old ssh.new 3a4 > addkeystoagent false 36d36 < useprivilegedport no 47,49c47,50 < hostkeyalgorithms