I have three different Sonos setups at different locations that used to work with just one phone and one app - and the old app would automatically switch between the different systems.
The new app broke this. The new app appears to no longer support multiple physically separate Sonos systems on separate networks that are all linked to the same user ID/controller.
I tried to reset the devices at my office and re-add them, but that made matters worse. I now get “there was a problem linking ... to your account” and the speakers appear to be just bricks. Even after a total reset, I cannot re-add the speakers at all.
This may be the most incompetent consumer technology company in the history of mankind.