fail2ban not banning IPs on Ubuntu 20.04

Solution 1:

For anyone who finds this a few months after the thread died, I hit the same problem on a new 20.04 server install while following most write-ups.

I solved it by explicitly setting:

sshd_backend = systemd

In my [sshd] section of jails.local.

The default (pynotify) was incorrect for that system or had some deeper issue stopping it from functioning as expected.