I have the same issue described in this old thread: https://community.norton.com/en/comment/8145261. That is, when the PCs attempt to do UPnP communication with the router (e.g. at http://unifi:8080/upnp), they're getting stopped by Norton Family as that's an "uncategorized" website.
I could resolve this by whitelisting this URL, however when I try to do so I get the error "invalid website", I assume because it doesn't have a .com/.org/etc. top level domain. But it is a valid website on the local network, and I would like to whitelist it so it stops getting blocked.