Do you mean web content filter?
It has an option to block access to web sites using IP. Some antivirus get their updates via direct access to IP so deactivating it may help:
Can you check which ports are used incoming/outgoing via /var/log/firewall.log to see which ports are blocked?
You may also check it on your computer with LTE.
Sorry, I still don’t get how this Gravityzone thing works. Is it just an antivirus client or does it have an internal management server which needs the open ports for internal network?