I would definitely submit a diagnostic report if this happens again, ideally within 20 minutes of it happening, and post any/all the diagnostic references back here. It may also be best to contact/chat to Sonos Support staff via this LINK.

Thanks Ken. I did try calling but that is office hours. I hadn't realised until after that there was a 24/7 chat facility. I will do as you say when/if it occurs again and post the outcome. After I posted the Q, I powered off all of the connected Sonos equipment and switch on again. There was no repetition of the issue, though it would have to be longer for me to be confident the issue was cleared.
 

I’ve had the exact same issue on Beam Gen 2. Same….Apple TV playing Atmos audio. The 24/7 chat is a bot…..totally a waste of time with this kind of problem. I am rethinking my allegiance to Sonos. Seems their products and software are going downhill. 

Wow. One occurance of a problem and Sonos is going downhill? Should you nog at least give Sonos a chance to solve this?

@106rallye Do a search of the word “popping” on the troubleshooting board. That will help you understand better how many people are struggling with this issue. 

You also must have read that Sonos advises to call them if this happens. Have you done that?

Hi, 

I bought a pair of Sony xm4 headphones yesterday and suffered the same issue, which had me thinking overnight. 

I think I have sussed out a work around to stop whichever Sonos sound bar cutting in, after a couple of seconds of Bluetooth headphone sound. Forgive me if this is elsewhere on the forum and I am repeating something that has long since been known. I just haven't read all of the stuff that's been posted but clearly from what I have read, it has remained an issue for some, as until this morning it was for me. 

Firstly, I own a ‘18 LG 65 wallpaper TV with which I found that switching off the Simplink hdmi cec toggle in All settings/general, then selecting Bluetooth device in the usual way the headset should connect and remain so. To revert to the soundbar turn Simplink back on. 

However and secondly, this did not work with my ‘21 LG 77 C1 set. I remembered from the initial TV set up, that there was a eArc toggle buried in settings and this turned out to be the key. 

Therefore;

All settings (3 vertical dots)/sound/hdmi setting, then toggle Simplink HDMI CEC to off.

come out of ‘all settings’ then change sound source to Bluetooth and connect device in normal way. When you want to revert, first turn Simplink back on  and then toggle eArc to 'on’ (it won't work the other way around because eArc is greyed out. 
 

This is far from ideal and still requires some fannying about with settings but at least it's better than physically disconnecting power or hdmi cables which in my case and no doubt many, can be very awkward and in any case, I understand that  hdmi is not supposed to be routinely plugged in and out.
 

I haven't lived with doing this yet and it maybe that Simplink turns itself back on when the TV is turned on and off (the eArc will not btw) but hope this helps someone out.