(Debian 9 installation)
I think I might have spotted a bug since one of the latest updates.
fail2ban seems to be properly installed and configured but does not start anymore when the server (re)boots.
Manual starting works fine.
Webmin's "Bootup and Shutdown" does not help: fail2ban is marked as "Start at boot" ... but still does'nt.
Webmin's "Fail2Ban Intrusion Detector" does not help either: changing the "Start at boot" leaves the option on "no".
All the best, Nico