First I've heard that one. Maybe uninstall and reinstall the App to see if it was corrupted? 

Once that is  done force an update check to make sure all Sonos are current. 

I’d be tempted to also reboot / power cycle the speakers. 

I rebooted everything, and all components have the latest updates. Upon further investigation, I determined it was only shutting down the Sonos Arc (arc, subwoofer, surround sound in great room) when I adjusted the volume, apparently because it is also tied to the TV. Even though nothing is playing on the TV (displaying security cameras), it apparently is interfering with the arc. When I turn TV totally off, the problem goes away. I can live with it, but it just started doing it with the last app update for some reason. Thanks!

You  might look at the TV Autoplay setting, under home theater and see if turning it off removes the security video issues.

We use it when we have a fireplace video playing but want to stream music.

OK, I'll look at that. Thanks!

Hi ​@Groff5 

Welcome to the Sonos Community!

Sorry to hear of this issue you are having with your Arc Ultra’s room going silent when you try to adjust the volume.

If this issue is as repeatable as it sounds, I’d ask you to please get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports - if there is an issue that needs addressed on our side of things, this will be the only way that we can identify that fact and start work.

Thanks.