Not sure if you have the same issue but one of my R3s got stuck after my router crashed, and was unable to connect to WiFi, even though Multiroom saw it.
Hold down its + and - buttons together until the lady says "resetting the speaker", it should fix it.
The app can find the 3 speakers and can even group them. But, when I tryck to group them as a surround group it just cant even start the process. I have reset the soundbar and my 2 R-lights. It doesnt fix it. I remember reading something about just some channels are working with the system in the 5GHz networks. But cant find that post.
Can you see all three speakers in the multiroom app?
They all need to be on the same WiFi channel - if you go to: Settings / Advanced Settings / Network Status the app will tell you which channel each device is on - if they dont match then that is where the problem lies...