Is this server running a recent version of Ubuntu and using systemd? Also, have you verified that fail2ban actually blocks you by intentionally making bad login attempts to trigger a ban? I do this with every new machine and never assume it works until I can trigger it on demand. (test using a VPN or set a very short bantime so you don't lock yourself out)

I ask because systemd may not be writing the failed login attempts to the log file fail2ban monitors, which means fail2ban may not be responding to attacks. I don't recall exactly how I resolved this, but I think I had to set "backend = systemd" in my jail.local under the [DEFAULT] section header.