I had two PLAYBARs that did not show this behavior. They were connected to Vizio TVs.
I’d probably try several things, and test between each.
First, a simple power cycle of the Sonos PLAYBAR, by unplugging it from the wall for a couple of minutes. I’d be tempted, given the nature of some capacitors (I have no idea if Sonos uses them) to go longer than two minutes. Essentially unplugging the PLAYBAR, and then do some other chore for half an hour, and then come back and plug it back in.
Next, I’d do the same power cycle process to the TV set. After that power cycle, I’d look at the audio settings to be sure the TV was set to ‘fixed’ on any digital/optical output, just in case. Many TVs (perhaps most?) don’t have this setting, but it’s worth checking, just in case.
Third, and most ‘destructive’, is a step I’m only recommending because you say you have other Sonos equipment. If this was the only Sonos device in your home, I’d let Sonos reps make the call, but in your case, I’d try a factory reset of the PLAYBAR, to force a new copy of the OS to get loaded.
Finally, if none of those work, 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.
