First, my bona fides: I suffer from this issue as well and experience exactly where described in The Martian, etc. I’m the guy who posted the bug report with the Google EXO player.
Just thought I’d check in and also post that I believe perhaps the best/easiest test is just to watch a rip of the 4K disc of The Empire Strikes Back. It’s only a momentary glitch, but at 1m 15s into the movie (during the opening title crawl), the sound cuts out for a moment. It doesn’t seem to lose sync at this point, but there are more glitches further into the movie. The opening crawl, I believe, are where a lot of seamless branching takes place in order to accommodate various languages.
Whenever I wonder if an update might have fixed the issue, I just watch the opening crawl to Empire. 
Man, it really does seem like. . . between this and the sound-sync issues on Apple TV, you just can’t get a good Plex playback device these days.
