Not having any SSH troubleshooting experience I didn't know where to start. I installed
Webmin to give myself a head start and clicking on
Servers | SSH Server I saw a rather self explanatory button:
Start Server.
Not sure how or why SSH was turned off, perhaps it's one of
systemd's [ahem] innovations...I'm sure there's a very simple command line, like
sudo systemctl start ssh.service...but actually I remember this not working...goddamn
Google says it's
sshd.
I actually built a new server (a second test server which I have been meaning to do as a sandbox ofr ages) and replicated this problem out-of-the-box, at least I know it's easy to fix and if all else fails
Webmin can do it for me. Maybe someone else will find this thread of three posts useful.