Looks like this might be the same case as T410009 (except that I don't use vscode server and I'm not sure where the other sessions come from).
$ ssh -v jberkel@login.toolforge.org debug1: Connecting to login.toolforge.org port 22. debug1: Connection established. ... Authenticated to login.toolforge.org ([2a02:ec80:a000:1::1c5]:22) using "publickey". debug1: channel 0: new session [client-session] (inactive timeout: 0) debug1: Requesting no-more-sessions@openssh.com debug1: Entering interactive session. debug1: pledge: filesystem
and then it just hangs.