In my network infrastructure, my Unifi XG-8 is the router/firewall but the way it works is that each of the 8 10G ports are separate LANs. I have a single LAN setup going to a distribution switch - a Unifi XG-16 - that everything hangs off of either directly or indirectly (through other switches). If I hook the Nucleus+ to the router I’d have to create another LAN and then bridge the 2 LANs and I think that adds more variables to the mix.
I think the best next step would be to hook the Nucleus+ to the XG-16 and see what happens. Do you agree? I can try this tomorrow.