Please re-enable debug, but not verbose, level logging.
When disabled it removes valuable information from the server log files.
Settings → Server_Name → General + Show Advanced
This problem crops up occasionally (see thread below). I’ve never seen a solid diagnosis or resolution.
Some threads suggest it is related to Plex remuxing the stream, which happens when the audio is transcoded.
What happens when you play the movie with Dolby Digital / AC3 instead of TrueHD audio and without subtitles?
Does Plex direct play the movie?
You can monitor playback via Plex Dashboard → Now Playing + Expanded View. That will show if the video or audio is direct playing, direct streaming, or transcoding.
