What did Sonos Customer Support say when you called in with that diagnostic number? 

Sure wish those of us who aren’t Sonos employees could see that data. You’ve already done all the things I would anecdotally suggest. 

@DukeOfHavoc Try this in this specific order:

Disconnect everything from the TV and unplug the Arc and TV from power for a couple of minutes. Plug everything back in but keep everything disconnected. Make sure Simplink is enabled in the TV settings. Run TV Setup in the Sonos app and follow the app instructions. When the app instructs you, connect the Arc to the TV’s HDMI ARC port using the Sonos-supplied HDMI cable. After the Arc has been successfully connected, connect any other devices to the TV. Also be sure that TV Autoplay is enabled in the Sonos app.

Hi, Superstar

Thanks for taking the time to write this all out. Just followed your instructions to the letter but alas it still doesn't work. If I toggle eArc on and off, I get a couple of seconds of audio and then it disappears. 

Really appreciate you trying to help. I'm getting very frustrated with this. 

Ah, I haven't called them. From looking at the forum, I thought the procedure was to send the report and then log something here. I will try and call them today to get an answer. I fear I'm going to get the dreaded "you need to speak to your TV manufacturer" response. 

I had the same issue since last week. Really frustrating. Now I only can’t use the volume/mute on the magic remote any more. I need to use a second remote instead. I think it has to do with the last LG update. 

Do you have sound coming out of it though?

Yes, but you have to put the volume to the max for some reason. 

Weird.

They've asked me to test with Optical Out but I don't have the adaptor anymore. Also they want me to plug it into the ethernet port. Really not sure that's gonna make a difference though. 

Update:

If I do a full unplug, I then turn everything back on but the Arc but I have the HDMI plugged into the LG eArc. I then turn the Arc on and the TV asks if I want to switch to the sound bar and it works...for a while. I did this yesterdy and it lasted maybe 20 minutes. 

I’ve done it tonight and its working again. I’ve taken a diagnostic report: 26688067 (should Sonos actually come across this) and I will call them tomorrow to see how that compares the previous ones I did for them when I was on the phone.

They have asked me to test it with a friend’s TV or use the optical cable not neither of those are sadly an option for me. 

There are extraordinarily fewer forum moderators than CS folks that work the phones. 

@DukeOfHavoc,

I’ve seen this issue reported before with this make/model of TV and it turned out to be an Amazon Fire TV stick connected to one of the HDMI ports stealing CEC focus. Is there anything else connected to the (other) HDMI ports 1, 3 or 4? If so, remove those temporarily and see if that makes a difference. 

Hiya, Ken.

Thanks for the comment. Up until last week, I always had my PS4 plugged in but since this issue, I’ve not had anything else plugged in. 

It lasted around 2 hours tonight before the sound just decided to stop working. Nothing changes on screen, the TV can still see the Arc, it just stops transmitting sound. 

It certainly sounds like a HDMI CEC issue, but whether it’s the TV, HDMI cable(s), or Sonos Arc hardware/software that’s faulty here, is difficult to say at the moment. I see you have tried a full TV reset. have changed the HDMI cable and that you tried a factory reset of the Arc too?

My own thoughts are it really would be helpful to try the Arc with another TV, as that might help point the finger in a particular direction, or you might want to consider the factory reset(s) again.. but I know what a PITA that is to do.

Had the exact same problem described on my LG OLED after a TV firmware update.  Easy solution for me..eARC somehow got turned off.  Go to sound settings (it will say you can’t use them with HDMI ARC on) and scroll to bottom.  eARC needs to be selected and the ARC immediately works as always.