There are issues with Audio/Frame sync with almost every movie that has multiple versions on one disc ripped/backed up. Examples include: Fast 9, The Martian, Halloween Kills.
UHD (or standard bluray) movies that include both a Standard Edition/ Extended or Directors Cut have issues with playback (seems to only effect ones with Atmos). There are tons of discussions about this on other forums, and apparently it is how Plex deals with MKV Containers and seamless branching. People who use other players like VLC or even Kodi (with plex) have no issues with playback. ONLY when using the Plex Client (with the plex player) does the issues pop up.
