Make sure you have updated the firmware on your LG CX.

You should be using the Dolby Atmos Bitstream output. If sync issues persist, what content are you playing on your Xbox exactly when this happens?

Thanks! I have upgraded the firmware. I'm using bitstream Atmos. I thought that 7.1 uncompressed might be better. 

Thanks for your help. 

The audio options on the TV are not half confusing. 

Sorry I can’t be more help. My LG C9 is attached to the wall of my office in Xbox Central, where I am very much not. While I can easily access my office Xboxes remotely to change settings etc, I cannot see or hear the TV remotely to see what affect they have on it.

My understanding of HDMI audio is low (I work on a totally unrelated area in Xbox) so I cannot recommend further.

I only have Playbars at home (and my LG is ancient), so I cannot experiment with HDMI audio here.

Experiencing a sound sync issue also with the same set up (CX, Arc, and XBOX series when using the Kody app on Xbox.

Luckily, there’s an option to sync the sound backwards in Kodi (Unlike in the Arc or LG settings which only allows syncing it forward).

However, I suspect I have issues with the built in Youtube app on the CX where the audio is out of sync. I can’t fix that.

I’m really disappointed with the compatibility of the LG CX and Sonos Arc. Had I known better I wouldn’t have purchased the sound bar. I won’t recommend it to anyone going forward.

All I need is the option to sync the delay backwards in an easy way. The app currently only allows syncing it forward, and in an unclear way in the “TV Dialog Sync” menu.

Also, it’s sooo unclear: +1 to +5 - what does that stand for? why not give us a way to adjust it by using seconds or milliseconds?

Of course that if LG would have given that option it would also solve the issue.

Yeah I thought eARC was supposed to sort all this. 

What output audio is your xbox set to, and what have you got the hdmi audio format and eARC set to on the TV?

To be honest, I feel a but silly now.

I tried so many different configurations and workarounds, but didn't revert to the most basic troubleshooting step...

Disconnecting and reconnecting to the electricity seemed to resolve all the issues but the Kodi sync, which i have an acceptable workaround to.

I tested the sync using a youtube audio video sync video on native Youtube app and on the XBox youtube app, also tested a video on ScreenShare. so it's quite confirmed.

If I see that the issue is resolved as soon as a couple of days pass, i'll take my words back.

Now I returned the TV audio settings to eArc and Automatic configurations.

Xbox HdMi audio is set to bitstream out, Dolby Atmos.

Hi Obi-Wan Aloni,

Thanks a lot for posting this. I couldn’t imagine this could work, but I tried it and it is for sure much better somehow. At first the delay was massive, now I’m not even sure there is a delay. Maybe very slightly. But I’m not even sure, so that’s a massive improvement! 
 

I took out both TV (C9), Xbox SX and Sonos Arc for about a minute. Didn’t change anything. Settings bitstream out, Dolby Atmos. TV on eARC pass-through. 

That is what Sonos says to try first, keeping my fingers crossed! 

Any update?  Is your issue resolved?

I currently use uncompressed 5.1 on my series x, I only use the console for games and not all games support atmos anyway.

I have LG B9, Xbox Series X and few days ago I bought Sonos Arc. I set Xbox to Bitstream and Dolby Atmos (it wanted to download Atmos app to my xbox and some kind of registration). 
I have absolutely no problem with sync. Dialogs in games are synced and even Youtube on Xbox is working great - no sync issue (or if there is delay it is really minimal and not very noticable).
Maybe there was an update:) I just wanted to notice new users that in my case no problem with Arc and sound is beautiful! 

Note about uncomressed 5.1 - if I select this on my Xbox Series X the sound is dull and tiny - don’t like it. Dolby Digital was much better option. But Dolby Atmos is the best.

Note about eArc on TV - I had to turn on eARC in settings of my TV! By default it was turned off and worked as old ARC port