Periodically, my Sonos systems gets into a state where the volume reverts to zero (mute) whenever I try to turn it up. I think this is mostly when I am using Spotify Direct, but I am not sure about that. It has happened multiple times and I have friends with the same periodic problem. I just caught one live and took a video screen capture of it happening on my Mac.
Sonos diagnostic 7395506 was taken when the system was in this state.
Same problem on my iPhone interface. The problem was resolved by resetting the controller from my Mac.
Best answer by Tom B
Hi FergiDotCom, this does indeed look like the lock screen controls issue. Spotify is working on this right now and will likely have a new version of their app coming to the app store soon. For now, just disable to hardware volume controls for the Sonos app on your iOS devices. Otherwise, just make sure your Spotify app is kept up-to-date and Spotify will have it solved as soon as they can.