1. Plesk performance is slow.
ERROR:f2bmng:Timeout of 10 seconds has been reached. Lock 'service.fail2ban' is already owned by another process with pid <unknown>
ERR [panel] Going to on for Db_Table_Row_Service_Package
ERR [util_exec] proc_close() failed ['/usr/local/psa/admin/bin/f2bmng' '--status'] with exit code 
ERR  '/usr/local/psa/admin/bin/f2bmng' '--status' failed with code 1.
3. Running simple procedure in Plesk like refreshing IP address in Tools & Settings > > IP Addresses > Reread IP cause 504 error after 15 minutes waiting.
Corrupted Fail2ban installation.