Google Wifi/Nest Wifi Help - NM Fixed Randomly

I've been running the old 3 puck Google WiFi setup for a couple years.

Bought a new Google Nest Router.

Followed the instructions and factory reset the original 3 pucks.

Gave my new Nest Wifi Router same network name/pass (first potential issue?).

Reconnected the other 2 Google WiFi points no problem.

However, the Google WiFi puck that used to be a router won't finish setup. I get a long "Something went wrong.." message on the "Creating Wifi network" screen. I feel like it's obvious its former status as the router is the problem, but since I've already factory restarted it through the app and manually I'm not sure what else to do.

ETA: lol of course when I do it all again for the 10th time it finally connected