No sound with Sonos Arc sound bar

I have a TCL Android TV with the Apple TV app installed, and a Sonos Arc sound bar connected to the HDMI-ARC on the TV (not an e-arc connector)

some movies play fine, but others have no sound. If I start the movie playing, then unplug the Sonos from the mains power, sound starts playing from the TV speakers. I then plug the Sonos back in to power, it boots up, sound pauses, then sound starts playing via the Sonos - perfect lip-sync, the Sonos app reports Dolby digital 5.1, or Dolby atmos (DD+), whatever the movie is, no further issues. I can pause the movie, rewind it, still the sound works fine.

Movies in plain stereo always work fine without needing to unplug, but so do some movies with atmos or 5.1., it seems to be totally random which work and which don’t.

if I unplug and re plug the Sonos before I open the Apple TV app, or when it is at the Home Screen, this doesn’t work - the movie has to be actually playing for the reboot trick to work. Change the movie, and again no sound, I have to go through the unplugging step whilst the new movie is playing.

sometimes unplugging the Sonos whilst on the Apple TV app Home Screen will cause the app to crash, and go back to the main android tv screen.

I’m on the latest android version available for the TV (version 9.0), have uninstalled and reinstalled the Apple tv app, and updated the Sonos software.

so I don’t know if it’s an Apple TV app issue, a Sonos issue, or an android issue. Starting the movie then immediately rebooting the Sonos by unplugging it is a simple solution that works, but it would be nice to have a permanent fix.