Try this:

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.

I have a similar problem.  I’ve spent countless hours on chat tech support and phone tech support.  they haven’t been able to fix the problem.  If I can stream music from the app, is it possible there’s a problem with the HDMI port on the Arc?  Is there a way to test the port?  the diagnostics from Sonos show the port is not connecting to the tv.  I’ve followed the steps shown above.  Is there a US based company that repairs ARCs? 

Yes, it is possible.

Connect another HDMI ARC generating device to test…most likely another TV. The TV is generating the ARC signal, not your source device (cable box, DVD player, etc).

Im not aware of any ‘authorized’ repair facilities here in the US. I would suspect there are likely many non-authorized repair facilities, but I’ve never needed to look at it. I’d think any competent TV related repair shop could fix an HDMI port…assuming that’s what the problem actually is. It’s possible it is, but I would expect the issue is somewhere else, and wouldn’t want to break warranty  to get my Arc cracked open and a part that wasn’t broken ‘fixed’. 

Frankly, if it was my money, I’d bet on the CEC ‘computer’ in the TV is broken, in some way, not the Arc. 

We cannot rule out a hardware issue with the TV or ARC.

Home testing HDMI-eARC is not practical because there are no inexpensive testers. You could try connecting ARC to another TV.

Make sure that the HDMI cables are fully seated in their sockets. Sometimes there is slightly increased insertion back pressure near the end of travel causing the user to assume the plug is fully seated, but it is not yet fully seated.

Thanks for the replies

 I’ve taken these steps

1. under a tv extended warranty the tv mother board was replaced which included the HDMI Arc port.  Wouldn’t the CEC “computer” be included on the mother board?
2. I replaced the HDMI cable with a new one from Sonos
3. i have another LG tv with an arc port. I tried connecting the sound bar to the TV.  Same issue
4. i’ve ordered from Sonos an optical cable to see if connecting the sound bar to the tv’s optical port will address the issue