My set up is a Roamio with several Mini's. It's a mixed network, with some connecting via Moca and some via ethernet. It has worked well for many years.
One Mini stopped working, so a purchased a new 9300 Mini on eBay. After some delay on their end, Tivo added the Mini to my account and I see it in "My Devices" on their website.

I simply cannot get the Mini to connect to the Roamio. When the set up process gets past the "call in" phase, I get an error saying it can't find a suitable DVR to connect to. I tried forcing multiple updates on both the Tivo and Roamio, waiting between attempts to allow Tivo's database to update. I have restarted both devices and my router multiple times, and I have tried connecting the Mini to different ethernet to different ports/locations in my house. I also tried giving the Mini and Roamio static IP address in my home network. Other Minis are still working fine.

I also tried connecting the mini directly to the router via ethernet and directly to the Moca network with a short cable.

No luck. I tried Tivo tech support but they are not helpful and just read a script saying to reboot the devices and the network hardware. I've done that at least 15 times.
Any thoughts?