A while ago, I noticed an issue with the latency indicators in Unifi Network on my UDM Pro. The values for Microsoft and Google were showing N/A, though the Cloudflare one was working fine. Originally, I hadn’t paid much mind to it but recently Ubiquiti added an ISP Viewer in Site Manager and that UDM wasn’t showing up in the list. I figured the broken latency measurements had something to do with it and decided it was time to figure out what the problem was.
Some searching around lead me to this community post with someone experiencing the exact same issue. Comments in that thread seemed to indicate the issue was caused by DNS (it’s always DNS) and possibly the WAN failover functionality. Checking my own settings, I had WAN1 DNS (Settings -> Internet -> Primary (WAN1) -> IPv4 Config -> DNS Server) set to Auto. I decided to start with the easy option and switched it off Auto and set Cloudflare’s DNS (1.1.1.1) as the Primary Server.
Sure enough, that did the trick!
Interestingly, setting it back to Auto didn’t cause it to break again (lending credence to the issue having something to do with WAN failover). I ultimately decided to leave it set to Cloudflare to (hopefully) prevent the issue from popping up again in the future.