The ban and unban is ok, its the purpose of fail2ban and the log file shows that it works as intended. Fail2ban bans a ip if there are too many failed login attemps from that ip and it eill unban the ip after some time to avoid that your users get blocked permanently. This is useful and nescessary this does not has to be an attack, it can simply be a normal ftp client were soeone entered a wrong password which tries to auto reconnect.
Banning aind unbanning is done with iptables, so you can ban ips also manually. Your lient ip should already be unbanned as the ban time on your server is most likely 10 minutes.