Hello…. Just moved into a house that has an Arc, as well as an amp. Did factory resets/transferred ownership to me no issues. 
Now I’d like to add my mini-sub. Went through the same process, minus the transfer, says it’s connected to the system, but will NOT get assigned to the room group w the Arc

¿compatibility issue? It’s seems to drop from the system now as well. No router/connection interference that I can tell. Thanks for all input!