Hi,
This is a bug report.
I have been using Plex for about a year now on many different platforms, but within the last few weeks my Samsung TV (model UE50KU6075XXE - bought in January 2017) has displayed subtitles out of sync - sometimes up to 10-20 seconds off. This does not happen when watching the movie from the beginning; only when resuming a movie in a later session. Sometimes it fixes it (or at least gets better) if I toggle the subtitle language within the app or stop and the start the movie again. Note that when I do this on other platforms (e.g. Android or Chromecast) the subtitles work fine and are in perfect sync. Note also that I have only tried this with external .srt files - it may also occur of internal subtitles but I have not tried that.
It seems that the out-of-sync offset is related to the time it takes to start the movie. So if the server is slow to react the out-of-sync offset is bigger.
I am running latest server on my QNAP NAS (1.5.5.3634) and the TV auto updates to latest version of the client.
Please let me know if you need any other information or let me know if there is anything I can do.
Thank you.