fail2ban now supports IPv6 - please upgrade
At some time you closed the request "fail2ban for IPv6" stating that fail2ban does not support it. That was no doubt correct at the time - but now it does, see https://github.com/fail2ban/fail2ban/tree/0.10
I'm seeing a lot of warnings in the fail2ban log on my dual stack servers, like this:
66:1000:b01c:10ab:0:1: [Errno -9] Address family for hostname not supported
and my log checking software is complaining to me about the overly long fail2ban log.
See also: https://ctrl.blog/entry/fail2ban-ipv6
Available since Plesk Onyx 17.9 Preview 7.