Just chiming in as a LG 65E6P with a Marantz SR7011 receiver (everything hooked through that, then into the ARC HDMI of the TV) who's had the same sort of issues and pulled my hair out for quite a while over them. I've got workarounds for most things, although it's not ideal. Keep hoping a firmware update will fix it...
So far, this works for me:
- AppleTV Set to Match Dynamic Range & Frame Rate (BOTH)
- Auto Lip Sync On Receiver
For anything HDR or Dolby Vision, I'm best off using the built-in TV Netflix, VUDU, and Amazon Apps.
For anything SD, I'm just fine using AppleTV via iTunes purchases or Netflix (haven't tested Amazon a lot). It's whenever HDR or Dolby Vision is used that I have problems.
It's not ideal. I watched Shape of Water the other night, and the ONLY version with HDR was the Apple version - Vudu and other stores had it, but in SD seemingly. Since there's no way to watch the best version other than AppleTV, I had to lock frame rate at 60Hz via AppleTV to get the sound to work right. For that particular movie, since most of it is slower, it didn't make that much of a difference, but for a fast action movie, I definitely would have preferred 24fps (and honestly would prefer it for everything if I could get it to work properly). It's unfortunately a pick and choose game at this point.
I should also note I briefly played with routing the AppleTV through the TV and have ARC handle the sound, which helped a lot of issues, but introduced an unfixable one that ended up seeming worse - namely, the picture was just slightly before the sound (at least for SD content), and there was no adjustment anywhere that could fix it.
Frustrating. I do think it's the fault of the TV, only because I have problems with SD content sound sync in Netflix on the TV apps as well as Youtube. I also haven't heard a ton of reports of this with other models of TV. So I don't know. I love certain aspects of my TV, but between these audio issues and some burn-in that I got, it may not be something I have long-term, which is sad because the picture quality is awesome most of the time.
P.S. I know I could use the receiver to add delay for things like that Shape of Water situation, but I never feel like I can get it exact, and it always bothers me to the point I'm focusing on whether I think sound is in sync instead of the movie. Just setting to 60 produces less anxiety. =oP