Fail2ban is really dumb. It looks for failed authorization attempts from remote hosts, and then bans them. So I'm guessing that, for some reason, they're trying to authenticate to you with invalid credentials, fail2ban is picking that up, and blocking them.
Firewall is much smarter, and doesn't do that. Sadly, fail2ban is really annoying about jumping in front of Firewall and blocking things that it shouldn't. It's on my list of things to care about.