Great, that a Sonos entity is showing the cover-image of a song just playing.
But when switching to a Radio-station (e.g. from myTuner Radio), the Remote3 is still showing the cover-image of the song played from a local NAS or streaming-service.
This seems to be a bug. Or missed I some configuration?
I had the same issue. It only changed when I tapped at the top of the screen and went in to the ‘fix states’ screen and exited. It then updated. As you say I think this may be a bug.