There must be something else during installation process.
I uninstalled and installed again but there is something wrong:
/usr/bin/fail2ban-client points to /usr/local/bin/fail2ban-client that does not exist.
When I'm doing
sudo find / -iname fail2ban-client, the only result I have is
/usr/bin/fail2ban-client. Considering that this is a link, it means that fail2ban-client is nowhere on disk. I believe that aapanel relies on some configuration for installation and that this configuration is not in sync anymore with what is really installed. That's my best guess.
Any other idea how I could really reset completely this fail2ban stuff?