Explicitly reserve the following ports:
echo '52220-52239' > /proc/sys/net/ipv4/ip_local_reserved_ports
Restart Imunify360 service and also the 3rd-party services have been affected, like eg MySQL.
systemctl restart imunify360
It's a known behavior with the WebShield which redirects the traffic to ports/connections that are not used by itself, therefore may block unrelated connections. The definitive fix for the issue already shipped with Imunify360 6.4 release.