Can’t say I’ve ever seen any TV/Arc lip-sync issues? I have my LG C9 TV set to pass-through the TV audio from any connected devices, like nvidia shield/fireTV etc. I only ever use ‘TV Dialog Sync’ if I’m playing from a Music App on the TV and want to group my Fives/Sub to the Arc/Era/Sub in the same physical room, but it’s quite rare I do that.
The things I really want for my setup are left/right balance controls for the Sonos HT rear/front surrounds and a different EQ setting for TV and Music audio playback.
If I had lip-sync issues then I would personally look to using an audio extractor for the connected TV devices, but it won’t solve the issue if these things are happening with the TV’s own built-in Apps - maybe in that case I would consider just using DD5.1 rather than Atmos audio, or perhaps (if the TV was over 5 years old) consider getting a newer TV with a decent/faster processor built in.
I like LG because their TV’s have a lip-sync feature built-in and they seem to have addressed the problem quite well compared to some other manufacturers IMHO.
I have LG’s also (3) with same settings and internal adjustments. As I said it happens only once in a great while which means too few occurrences to be concerned. It was just something I tried that worked so I thought I’d share. I also time shift a lot while viewing which may be factor on occasion.
After adjusting the Lip Sync in the Sonos app and still no Joy. Stop the AV stream either by turning the TV off or temporarily switching to another stream. I’ve found it fixes the issue 100% of the time when the Sonos app lip sync adjustment doesn’t correct the issue to my liking. I guess it resets the stream so to speak. So give it a try.. you have nothing to lose kind’a 
I would actually recommend restarting the AV stream, changing source, or just rebooting everything before you are modifying any lip sync settings for Sonos or your TV when the issue happens on rare occasions. Chances are that some sort of glitch got the audio off track slightly, and messing with the settings is just going to cause an issue after you’ve rebooted and ‘fixed the glitch’.
I’ve had rare issues of lip sync issues with my Shield/Samsung TV/Sonos Arc setup (plus HDFury stuff in the middle) and have always been able to resolve just by rebooting, usually the Shield only.
Rebooting as a first step is almost always a safe and easy thing to do before following other troubleshooting steps.
It’s not uncommon when jumping back and forth in a video. Some services/apps are more susceptible than others. The fault is in the TV or the video source device. Buffers get misaligned and simply need to be flushed and reset.
