Sonos Arc, Apple TV 4K and eARC setting on LG OLED C3

This morning I tried unplugging the cable box and Roku from the LG HDMI and the Apple TV worked fine.  As soon as I plugged in another device the sound problems returned.  Do you think that is a problem with the Apple TV not working well with other devices or the LG TV not handling multiple devices or something with the Sonos?  They all work with the Sonos unplugged and using the TV speakers but eARC is turned off automatically.

There was a link to send an email to the CEO of Sonos so I sent an email.   I was hoping to get a higher level of Sonos support but so far no response.  Do you think they really answer those emails?

No, I think there is a device that isn’t honoring CEC properly, which is being reflected in the ARC/eARC output. 

The last person I’d contact is Sonos’ CEO. The amount of time that they have to help troubleshoot is likely less than zero, and I’d expect them to hand off my issue to someone else. I’d instead be trying to resolve my concerns through Customer Support. While there could be an untrained person there, the chances of them actually helping my situation are much, much higher than any CEO, who’s job it is to make strategic decisions, not help users with an issue. 

This thread has helped assure me that I am not insane. Running into the same/similar issues. 
LG TV + Sonos Arc + AppleTV 4k 3rd edition. 

I just upgraded to an LG C2 (OLED77C2PUA) TV this week (from a 7 year old LG TV). On the old system, CEC and Arc worked seamlessly, but depending on the audio encoding, I’d get horrible lip sync / audio lag issues. Could be 2 different shows on Netflix - one Atmos the other not, and it would require different audio delay configurations in the TV and/or Sonos Arc settings to compensate.  Annoying. 

Setup my new TV and everything was synced gloriously… until you switch inputs and suddenly audio through the sonos died. 

My current config which seems to work perfect regardless of input is: 
 

Sonos Arc (updated to latest software)

TV: LG C2 OLED77C2PUA (updated to latest software)

Philips Hue Sync box (updated to latest software)

Apple TV 4K (updated to latest OS)

• Everything connected using 8k HDMI cables

Apple TV » Hue Sync Box (HDMI port 4) » TV (HMDI port 3)

TV » Sonos Arc (HDMI eARC port 2) 

Also have a Switch & and a PS5. Switch connects to the Hue Sync Box, the PS5 is direct to TV. Adding/removing these seems to have no effect. 

∴ LG TV sound settings: 

• Output: HDMI Arc Device
• ❌ “eARC support” on: no sound from Sonos
• 🟢  “eARC support” off: Sonos works

adjusting these seemed to have no effect

• Simplink is turned on
• Passthrough: Auto

∴ AppleTV Settings

• Audio set to Auto (not 16 bit)

∴ Philips Hue Sync Box Settings

Messing with these doesn’t seem to have an effect

• CEC Power State Detection: On
• New Input Detected: On
• HDMI Device Turns On: On for all 4 ports. 

Given what others have said here, I might try to turn on eARC support but turn off Simplink on the TV and see if that preserves the audio codec flexibility of eARC provides. I’ll post back later today when I get a chance to test. 

After a bunch more experimentation, the only thing that consistently works is leaving off “eARC support”. 
I get more consistent connections that way, but occasionally following an input change or waking from sleep, the TV will reset to “TV Speakers” and I have to update it to HDMI, and then it takes some time for the Sonos to wake. 

Sonos shows Atmos and all the other audio formats regardless of “eARC Support” being on or off; so not really sure what that toggle is doing.  I had thought that “eARC support” enables Atmos, and with it off it would only be limited to Dolby 5.1 or some older audio encoding—but that’s definitely not the case.  But… the moment I enable it, sound from the Sonos Arc is immediately disabled. 

I encountered this same problem with Apple TV 4K 3rd generation and Sonos Arc. However after several attempts and a lot of web research I believe the problem it’s on the LG TV side  I realized that if I change hdmi cables or disconnect my tv from power the arc wouldn’t get any sound from it with or without Apple TV. I had to disconnect all hdmi cables from tv and Arc. And both systems from power for a few minutes. And then do the Arc tv setup in order to trigger LG to recognize a new HDMI connection. Not flawless beacause I’ve already had to factory reset the tv 2 times in order to the TV recognise a new connection from Arc. 
By the way. My LG Tv it’s the Oled C3 model. 

Had this issue with a C3 and Apple TV latest gen. The fix for me was to make sure another device which was on was properly switched off (in this case a Sky box). If that was on, the ATV is silent. Bizarre glitch 

Same issue also here.

LG C3 with Apple TV 3rd gen, Fire Cube 3rd gen and Sonos Arc with Sub and Era 300s.

Connecting the Apple TV alone without the Fire Tv, and the 5.1 audio sources are playing fine.

As soon as I connect the Fire Tv, no audio anymore from the Apple TV. Only Atmos and stereo sources are working fine.

The only way to get the Apple TV 3rd gen to work properly is to shut-down the Fire TV.

Tried to reset everything. All HDMI cables certified 2.1. Tried also different of them.

Disconnected everything, power cycles on all the devices, waiting 30 minutes, reconnected: same problem.

Passthrough, Auto, tried all the audio settings from the C3.

Not really understanding why it’s not properly working.
 

Sounds like the Fire TV Cube is interrupting the normal discovery process for CEC, which is managed by your TV set. If you can, turn off CEC on your Fire TV Cube, or insert a CEC blocker in between it and the TV set, something like this. 

Unfortunately I tried already both of them:

• Disabling the CEC from the devices settings in the Fire Cube, Restarting then both the tv and the Fire Cube. Nothing.
• Bought the CEC blocker adapter. Same outcome.

You may want to contact Amazon, then, since based on your experimentation, the issue is with the Fire TV Cube, and not any of your other equipment.