Alright, so this lip sync problem has been driving me nuts for months. I finally stumbled across this page and I believe OP is correct. With an added bonus fix.
For reference my setup is LG C7, denon 4300, oppo 203 with one cable to the denon.
Real cinema definitely seems to be the problem. Based on the testing I just did over the last 30 minutes, I'm just going to leave it off all the time. I never have a problem with built in apps like netflix or hulu, only playing discs. The problem seemed to come and go with regular blu rays and made DV discs basically unwatchable for me. Turned real cinema off and it was like magic. I need to sit down and watch an entire movie, but for now I checked a few scenes on regular blu ray and then a couple scenes in It and all was well.
The bonus fix: To turn Real Cinema off on a DV disc, just set the picture mode on the LG to game. For me, the only other adjustment I made was moved white balance from W10 to W20 (I believe W10 is the default, pretty sure I never adjusted it). There might be further tweaks to improve quality but for now I'm just so relieved that the lip sync problem appears to be gone I don't even care.
Well, off to do some more testing.
edit: additionally set trumotion to user and dejudder to 1. was acceptable for me.