i followed this guide: https://www.howtoforge.com/tutorial...l-pureftpd-bind-postfix-doveot-and-ispconfig/
So the logs you show look like a clean start then stop. If you run 'service fail2ban start' manually, does it stay running? Maybe there's some service watcher that needs told that fail2ban should be started? I don't have ubuntu 16 offhand, and don't know if any such thing is found there (it's not on a typical debian install); ISPConfig has a 'Enable service monitoring and restart on failure' but I don't know if it tries to restart fail2ban offhand - if it does, see what you find running server.php manually with debugging enabled (see the 'please read before posting' sticky thread for instructions if needed).
