Sonos iOS app preventing muting of main iphone volume

If the Sonos app is open then the main volume of the iphone itself won’t mute.  Force quitting the Sonos app makes the phone volume mute work correctly again. It seems that when the Sonos app is open it’s running almost constantly in the background, eating up the phone battery and getting in the way of the phone volume control, but what’s it doing? I have all the permissions settings for the Sonos app off except local network access - no Bluetooth, background app refresh, location, notifications, microphone, Siri, nothing. The app and speakers are all up to date.  Are there any other settings I should look at if the problem could be my phone? If it’s another new app glitch I’ll just keep force quitting it every time I open it and keep waiting for Sonos to fix it like the other ongoing app things.