Had the same issues here - Sonos beam (GEN1) connected to OLED LG G2 with HDMI ARC, well recognized by the TV.

1. When connecting Bluetooth device (e.g. Apple Airpods Pro), it switches back to BEAM after a couple of seconds. Same when selecting the TV speakers, it switches back to BEAM automatically.
   ==> could not find any better alternative/solution than to turn off the CEC/Simplink in the TV settings to prevent the BEAM from taking control over the other audio devices/tv speakers.
   Not optimal solution though (because it forces you to change some TV settings before switching from BEAM to bluetooth device), but I can live with it.

2. When connecting other HDMI devices (e.g. satellite box) to the TV, it switched back to TV speakers. When selecting back again the BEAM as audio output, no sound coming out from the BEAM.
   Seems to be a conflict in HDMI ports, due to the CEC thing.
   I purchased a CEC less adapter on Amazon, connected it to the satellite box, and now it all works perfectly.

Obviously when buying these products (TV, soundbars, etc...) you don’t expect to encounter these kind of issues (I spent quite some time reading forums, also discussed over the phone with LG customer service, etc...), and you expect the manufacturers to solve this (be it TV manuf, Sound device manuf… I don’t care).
But in the end there are some workarounds that can be found.

Still, hope this helps for those who are still having issues.

It’s a Sonos issue. I also have a Yamaha soundbar. I swapped the soundbars to troubleshoot and no issue switching to Bluetooth when I use the Yamaha soundbar. My TVs are a Samsung UN82MU8000 series and a Sony XBR-75X850E.

I have 3 Samsung TVs, one with Arc, one with Amp, one with Beam. All have the problem, if I select a Bluetooth headphone or TV speakers, they revert back to Sonos within 2 seconds.

it is terrible, Sonos, if you cannot fix it, it would be appreciated that you write why in this thread

Can you link what adaptor you use? 

Sonos is acting like a web browser: it wants to be the default sound output. 
 

I found a simple solution: I returned it to Costco.

It does baffle me this is still an issue. A simple On/Off button in the App would fix it. When you update the Arc it looses connection to the TV. So the mechanism of the Arc not ‘being connected’ exists. They just need to make it a button.

this one:

https://www.amazon.com/BlueRigger-HDMI-CEC-Less-Adapter/dp/B07BFL8TM8

but this one is also advised as alternative:

https://www.amazon.com/Lindy-HDMI-Adapter-Female-41232/dp/B00DL48KVI

I have the exact same issue. Very disappointed with Sonos. They could at least clealry communicate on this issue...

Yeah same here. This is a ridiculous issue. My previous soundbar didn’t have this issue, and I am considering returning my Beam.

the solution is also not working in my C1, CEC is immediately turned back on automatically by the Beam.

any other solutions out there?

Hi all, How about this method of switching Bluetooth?

Try switching between both when using Bluetooth sound, it's just a few steps, so ease your mind.

Go to Advanced Settings > Connections
Click on Device Settings Configuration
- Turn off the simple link
- Remove sonos in universal control

   - Not used, but removed just in case

Reasons:

Turn off the convenience feature that sonos automatically activates

Go to Advanced Settings > Connections

Click on sound

- Turn off eARC in additional settings

Reasons:

Simple Link will not start automatically the next time the power is turned on.

I use Air pod pro with lg OLE48cx and tried it with beam(gen2),thanks.

Supplementation.
If you wish to return to the sonos soundbar, please reverse this procedure.
When ARC is selected, Simple Link is automatically turned on.
This is probably because there are frequent problems with no sound if it is left off, so it is necessary to turn on the path so that there are no problems with manual connection in any home.
I am Japanese and not affiliated with LG or Sonos, but I would like to try the IKEA rear speakers from now on.

regards.

Simplink is the LG term for CEC. Samsung calls it Anynet, Sony calls is Bravia link (I think). Turning off CEC temporarily will solve this.

The jury is still out on this being a Sonos fault or just an effect of Sonos adhering to the CEC specs. There does seem to be anecdotal evidence other manufacturers soundbars do implement CEC differently than Sonos does on this point.

I am amaized that 3+ years and sonos could not connect their own product to a tv and try to replicate this, to see the issue themselves? I had my same experience and i imagine others will continue to have it! All smart tv pwners will see how bad sonos products are due to this 1 bug! Unless they dont set up another audio output.

It’s not a Sonos bug, it’s a TV bug.  My Toshiba Fire TV works just fine switching from Sonos to headphones and back.  My Samsung requires me to turn off CEC, and other people report they can’t switch back and forth at all for other brands of TVs.  So if it works 3 different ways with 3 different TV’s, it isn’t Sonos causing the problem. 

Hi there - 

Also, a very simple solution I discovered: make sure eARC is turned on. Was having the same issue with my LG/Sonos ARC after I unplugged and restarted some things. I noticed eARC was turned off and when I turned it back on, it stopped switching from Bluetooth to Soundbar.
 

Steps on LG TV: All Settings > Sound > Additional Settings > Turn on eARC at the bottom.

Then Sound Out > Bluetooth.

Should stick. Hopefully works for you too!

Hello there. It’s funny that when I’ve read the thread and it was 3yo when started I was sure that by the end of the thread an anew solution would come oute.(maybe it’s like the build in Alexa they have and it’s like only for 5countries?

Overall their products are very good I have to say that!

I used to have 1 beam and 2 ones while now I bought a new tv (QNED 86inch 866).

I did what TD2014 said(as the latest solution but nothing happened ofc)

I am testing it with Airpods Pro2.

is there any solution this could fixed with Apple TV?(highly doubt it but HAD TO ASK)

I guess I won’t be able to watch movie or play PS while my newborn is sleeping.

I can live with that but would be so good if i could

I have a LG C2 TV with Arc bought last week, and the same problem here. I am not able to turn off the simplelink while my Arc is connected via eARC port, its automatically switch back on. Its only works when disable eArc function on the TV an after I was able to turn off the HDMi-CEC function. For me it’s a big disappointment.

LG suggestion was to have the Arc connected via Optical port and will have no problem but for me it’s just meh… Atmos is not supported via optical port, but if I keep the Arc I have to accept that I wont be able to use for example Bluetooth headphone or etc.. nonsense . Actually it is related just with Lg C2 and Arc so its model related within a brand...

My LG C9 TV works fine switching from Sonos to headphones/Optical/etc...

Just turn on eARC in additional settings

I did and it worked fine, but honestly for me its not the best “solution”. As you know eARC gives you better audio quality, and lets see an example: 

I use my headphone and if I would like to swith from headphones back to the soundbar its automatically turn on the simplink again, which means I have to do the same settings again if I would like to use my headphone ----- go to HDMI settings turn off simplink and after that, I will be able to change my audio output--- and it is so elaborate. Tried with LG soundbar and it is worked perfectly, nothing has had to be changed.

By the way thanks for your time and advice but I sent it back, that is not how it’s supposed to work. Nobody could say if this is an LG or Sonos software bug, because it is a bug 

It’s not a ‘bug’ per se, it’s the way CEC was written. Neither LG nor Sonos own CEC, they just use the specification as an implementation point. But since the CEC control (computer) is in the TV set, and the Sonos is merely a client to that, I’d start the discussion with LG. 

I found a solution for most streaming services at least :)

Won’t work for live TV though.

Buy a Roku, I have a Roku Ultra which is great when using the arc. All of the Rokus have the streaming services: Netflix, Disney, Apple TV etc.

Link your headphones to the Roku. When you want to use them switch them on,  and select. All done! Sonos  out of the frame

I am getting the same problem with a new LG OLED TV OLED77C2PSC.AAU and SONOS (Soundbar Beam Gen 2]).

If I turn OFF HDMI-CEC on the TV, The Sonos soundbar turns HDMI-CEC back ON within a few seconds.
So it is is impossible to switch to the Optical Output for headphones, …
(Other than disconnecting the HDMI ARC cable physically)

There is no setting on the SONOS app to disable Sonos automatically tuning HDMI-CEC ON.

Very annoying, Given this problem has NOT been resolved in the past 2-3 years, I will be returning my SONOS Soundbar and giving bad reviews wherever possible.

There appear to be NO response from SONOS support on this forum.

I am getting the same problem with a new LG OLED TV OLED77C2PSC.AAU and SONOS (Soundbar Beam Gen 2]).

If I turn OFF HDMI-CEC on the TV, The Sonos soundbar turns HDMI-CEC back ON within a few seconds.

I was able to fix this problem by setting geARC Support]=Off before setting nSIMPLINK (HDMI-CEC)]=Off

For Headphones
1. >...]->&Sound]->&Advanced Settings]->&eARC Support](at bottom)=Off
2. >...]->&General]->&Devices]->&HDMI Settings]->&SIMPLINK (HDMI-CEC)]="Off" (Will goto TV speaker)
3. Mute TV speaker
4. >...]->&General]->&Sound]->&Sound Out]->&Use Wired Speaker]="Optical Out Device"

For Soundbar
1. >...]->&Sound]->&Advanced Settings]->&eARC Support](at bottom)=Off
2. >...]->&General]->&Sound]->&Sound Out]->&Use Wired Speaker]="HDMI(ARC) Device"

Still far too complicated, compared to simply replacing the SONOS Soundbar with another vendors sound bar.

Has anybody tried an HDMI CEC-blocker in line with the EARC lead to the Sonos Arc? In theory it should stop the Arc switching the tv.

I tried one off Amazon (Lindy) for around £9 and has solved the problem. No longer auto switches back to the Arc automatically.