I hesitate to even suggest this solution, as for many months my LG CX 55 inch OLED (OLED55CXAUA) randomly stopped outputting ARC audio to my [Sonos Beam Gen1 + Play:1x2] system requiring me to physically unplug the Beam’s HDMI cable from HDMI Port 2 on the TV multiple times a week. The TV would just output to its internal speakers while completely ignoring the Sonos setup until I re plugged it in. I was getting to the point of worrying about the TV’s HDMI port 2 getting worn out.
All prior suggested solutions on this website have been temporary at best, but I seem to have found a durable solution that has lasted me the past four weeks of regular usage, found by reading multiple posts about this issue and parsing together a solution through trial and error.
Of note, I first thought this was an Apple TV / LG CX / Beam problem, but I have realized after changing multiple settings on my Apple TV 4K Gen 2 (tvOS 15.1 with output forced to Dolby 5.1) over many months that it was a red herring because I was just using the Apple TV all the time as the source.
Ultimately, I believe that that LG and Beam are not playing nice through the HDMI-CEC protocols, specifically something to do with power. Sonos and LG engineering will need to figure this out.
First, my firmware versions:
LG CX: 04.30.10
Sonos system: 13.3
Second, my fix:
Gear button on LG remote → All Settings → Connection→ Device Connection Settings → Universal Control Settings → HDMI2(Arc) - > Manage Settings → Set Manually → Bluetooth / SoundBar → HDMI2 (ARC) → Yes to reset → DO NOT ENABLE “Auto Power Sync” (SIMPLINK is OK to be on) → Scroll down and select Sonos → Next → Done
The only thing that I have noticed different with this setting disabled is that my Apple TV remote’s power button now does not turn on the TV. I have to do this on the LG remote. For me this is a fair trade rather than having to be constantly annoyed that my supposedly first in class, rather expensive system is randomly not working.
To confirm this fix, two days ago I went back and re enabled Auto Power Sync and I had my first random disconnection in a month today.
At least for me, having Auto Power Sync disabled is the fix.
Hopefully this is a universal fix for others undergoing this same frustrating issue.