Since you’re using AirPlay 2, and not the Sonos controller, it’s liable to be an issue in your network somewhere. As a start, I’d unplug the Sonos devices from power, and the Apple TV, and reboot your router. Wait a couple of minutes before plugging back in the Apple TV first, followed by the Sonos devices. Give them both a couple of minutes to reboot, then check for software updates for both, and apply them. Finally, test. 

If this doesn’t fix the issue, you may want to 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.