Hard to be definitive, with only anecdotal data, but if the Arc works fine on so many other systems, my initial reaction would be a TV issue. Make sure that you’ve got the TV updated to the latest firmware, then reboot the TV by unplugging it from the wall for 5 minutes before plugging it back in.

If the behaviour continues after that, then I’d 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 Sonos system and network. 

Thanks for the reply, I will phone tomorrow.

I’ve disconnected every other device to leave these 2 , so 50/50 at least

Seems it is the tv