I didn't experienced this issue, can't figure out why this is happening. I checked the UFW status in terminal, it shows ufw inactive. then I checked in ISPCONFIG, it was showing as active, so I unchecked the enable status and saved. then checked it again and saved. Immediately all my connection to the server is lost. what could be the reason for that? I had it added all the ports for the firewall. I am attaching a snapshot, just before I enabled it.