Hi @mikey_s, welcome to the Sonos Community!

I’ve had a look into the diagnostics and don’t see anything that is specifically causing the audio to cut out. 

The HDMI connection can get in a faulty state that can cause audio issues, so lets power-cycle the TV by powering it off for two minutes, then back on again, to restart the HDMI handshake..

If you’re still having audio cut out, then I’d recommend having the Surrounds and Sub on a wireless connection instead of having everything in the system wired. While you have been fine with the system running like this previously, this may have always been a background issue but wasn’t noticed or was negligible.

As it’s only TV audio, not with music or with the solo Beam, it’s likely the signal is not reaching all Home Theater equipment in time. The Surrounds and Sub need to have a low latency due to the high bandwidth of TV audio. When everything is going through the router, other traffic can slow things down.

You’ll want to enable Wi-Fi on the Arc, Surrounds, and Sub, then head to Settings → System → Network → Manage Networks → Update Networks. This will add your wireless network to the Sonos system and allow you to remove the Ethernet cable from the Surrounds and Sub. 

This proposed solution with allow the Surrounds and Sub to communicate directly with the Arc with 5Ghz, rather than having to go through the router first.

I hope this information helps!

Just connect your Sonos Arc component to a NON-ARC port on TV. 

SOLVED with the provision that when you freshly turn on the system, the TV will complain that you need to connect to the TV ARC port. Just ignore that dialog and enjoy non - dropping of the soundbar as the designated output