Sounds like an HDMI-CEC sync issue. Check for updates for the TV’s OS, and try a power cycle of the TV by unplugging it from the wall for a couple of minutes. 
 

Might be worth re-seating the HDMI cables, or even trying another cable, on the offhand chance that the one you’re using is loose enough to lose temporary connection on the necessary pins, when a butterfly on the other side of the world beats its wings. Perhaps an exaggeration, but I did have an issue one time where trucks driving by would cause an issue on my TV.  Replacing the cable did wonders, and I had a spare cable lying around anyway. 

Definitely some kind of butterfly effect!  I re-seated the HDMI cable at the AMP side and we’re back to face melting audio.  Thanks for the assist, this was driving me nuts.  

I have the same issue with the same Samsung Frame TV. If I reboot the cable box, the Sonos Amp connects and TV sound is awesome. When I adjust the app, or turn the TV off, the sound connection is broken until I reboot the cable box again… Someone suggested getting a newer HDMI cable to solve the problem. Any thoughts?

I've had long-running problems with an LG C9 TV connected via HDMI ARC. The TV reports a sequence of errors on screen

"Wired connection lost” (TV reverts to internal speakers)

"Wired connection found

"SONOS now available” (SONOS connected-speakers get audio again)

This happens many times a day, irrespective of TV.

I have replaced the HDMI cable with one with a higher spec 2.1 cable..

I have tried disconnecting all other TV sources. 

I have had the same problem previously with an LG C7 TV.