>> I've also found that installing libpam-systemd seems to fix this for
>> me in my testing. (If I discover it still to be a problem, I'll post
>> again). However, I'd like to understand why libpam-systemd makes a
>> difference if anyone has any insight?
>
> It doesn't, I still have the problem occasionally on multiple systems,
> all with libpam-systemd installed.
> It's pure coincidence.
Interesting. The important thing here then is my question - WHY does libpam-systemd make a difference in some cases?
>> Finally, there are issues with using the ssh.socket approach which are
>> not at first apparent. When exiting an SSH session, all processes
>> created under that session are terminated - which means tools like
>> screen and tmux will not work. This may or may not be a problem for
>> you, but it's certainly means ssh.socket is also not a drop-in
>> replacement like ssh.service.
>
> please open a separate bug for this.
IMO this isn't a bug, it's intended behaviour of ssh.socket.