I believe this indicates the number of rooms in a group.  So a ‘1’ would indicate that the room is not currently grouped with any other rooms in your system.

Its actually the number of messages your speaker has that you haven’t read yet j/k

(I mean really, this simple UX change has confused so many people...)

Thanks. I’ll try grouping and see if the number changes.

It is one of the oddest changes I have seen in an app given that the normal indicator for a single something is nothing. 

The confusion also shows how few people read the Store notes for updates or the Sonos release notes.

Yet, I have no messages 

And once again sarcasm is completely missed, even with the j/k warning.