Have you physically moved the Sub to your basement? Do you have any other Sub already connected in the basement?

Hi, yes I moved the sub to the basement, where I did have a sub 3 installed for a short time.  I sold the sub 3 and don’t see any way to uninstall it from the app.  
the app easily allows me to connect to my living room Evo 300’s, but when I try to connect to the basement tv room, it states that no sub is found.  

Does the Arc Ultra still think the Sub (Gen3) is still bonded with it? Prior to selling the gen 3 did you remove it from the Arc Ultra?

I’d be tempted to factory reset the Arc Ultra, then see if you can add the Sub 4 to it afterwards.

It might be good to have a Feature Request to add an "Unbond a missing/broken Sub or surrounds.' to the App to remove the need for the factory reset in these situations.

I ended up factory resetting all three components:  the arc ultra, sub 4 and eco 300’s.  Everything is working perfectly now.  Thanks very much for your help!