Fail2ban doesn't work on Ubuntu 20.04. Why?

Question

linux

Greetings, dear ones. The problem happened. On Ubuntu 20.04 server, fail2ban does not work.

What attempts I just did not make, and -w deleted and added itptables-multiport and nothing really helps. Also, instead of iptables-multiport, I tried to install ufw. On 18.04 everything works with the same config, which does not work on 20.04. After some digging, I found out that in the new version of f2b they added f2b chains ON DEMAND. But having blocked my IP once with handles, no chains appeared. Can someone thread faced such a problem? In July, here, too, one guy asked a similar question, but there is no solution in his topic.

Answer 1

Show at least the output of iptables -nvL

Answer 2

Fail2ban refuses to add rules to iptables if "playful" pens write something to iptables.
First, we form the iptables rules, and then set Fail2ban (hardly delete and re-set - so that there are no traces). And even that didn't always work. With the help of iptables-save - it does not work, but for some reason it works through webmin.
Didn't really understand it.