How do you know there is no external interference? Going to a reduced volume is a lot different than cutting off completely. 

I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Valid point. Reminds me to pay attention to the old adage about “assume.” I’ll try that out and report later. Thanks. 

I have seen a few recent posts mentioning Sonos going to mute and seen that myself, not seen anything on just going to a low volume though.

Given the long queues at support I'd wait for another update or two and hope it got fixed unless it is really bugging you. If it is then do the diagnostic and call, it may get you a fix or at least let Sonos know to add it to the bug list.