No, was there a recent Philips TV firmware update perhaps?

Have you tried turning the TV off at the plug for five mins, then back on again in case it’s a TV issue? 

Not that I'm aware off, but will check. I guess, with all the recent problems it's easy to blame Sonos first :-) 

 Used to happen to me quite often a few months ago.       ( Sony TV - Arc via eARC ).  Tried all the usual suspects which did not work.   Ended up having to unplug the Arc soundbar to get it back.  Got to the point where I asked Sonos to allow Web access reboot again which at one point was an option.  Seems to have cleared itself up though. 
 

 My issue now is the Arc will Mute ( Green light ) when the TV is turned off ( probably normal behavior).  Sometimes when I turn on the TV the Arc does not come out of Mute.  No big deal; Just change volume.  Very often when the TV is off and I want to play music through the Arc-Sub-300s the Mute condition has to be turned off in the app to get sound.  Still no big deal.

 Sometimes the HDMI cable is at fault, but you have had success with your cable in the past so probably not.

 Still wish  //<sonos IP>:1400/reboot  was an option.

I have the same issue. My remotes (sky and Apple TV) both now revert to change the sound on the TV. 
 

i have to unplug hdmi in Sonos arc to get it working again. But this has to be done every time

anyone got a resolution to this? 

Since the solution to the issue in the first post was “power off, wait, power on”, have you tried that?

Also getting the same issue when switching to HDMI input on a Toshiba TV - have to unplug and replug that cable to get audio to SONOS Beam, was working totally fine up until iOS update 80.09.09. Not sure if there was a combined firmware update that has broken this, but also getting issues with surround distance since this update. Anecdotally it seems to have broken groups too. 

And again, since you don’t state whether you’ve tried it: the solution above was a tv power cycle. Have you tried that? 

Yes, no fix.

Yes. I have powered off, replaced HDMI cable, checked firmware for updates.