I’ve not used a UDMP yet, but I do use Unifi stuff. It sounds like a network misconfiguration somewhere. I’d be inclined to go through all your devices with static IPs and ensure the configs are all correct. I had a similar problem a while back and it turned out to be a typo on the network netmask on the router.
For most of my infrastructure stuff, I now use Static DHCP leases as it minimises errors when I fiddle.