Plesk is inaccessible from certain IP address, but the address is put to trusted list in Fail2Ban

Symptoms

• Plesk is inaccessible from some IP address (203.0.113.2, for example)
• IP address is whitelisted in Tools & Settings > IP Address Banning (Fail2Ban) > Trusted IP Addresses menu.
• Output of iptables -nvL --line-numbers | grep 203.0.113.2 doesn't list any DROP/REJECT actions
• Plesk is accessible from other IP addresses
• The ipset list command shows that IP is blacklisted:

# ipset list i360.ipv4.blacklist | grep 203.0.113.2
203.0.113.2 timeout 854950

Cause

IP address got blacklisted by Imunify firewall

Resolution

Unblock the IP in Imunify firewall. 

Alternatively, if the Imunify extension is disabled, but issue still occurs, perform the following actions:

1. Connect to the server via SSH

2. Remove the IP address from blacklist:

   # ipset del i360.ipv4.blacklist 203.0.113.2