Playing back movie with subtitle (SRT) causes pauses in playback (happens on Android and iOS too)

The topic says it all. If I turn of subtitles the movie plays back fine. This is on a PS4, but I see the same issue when using subtitles in the iOS and Android Plex apps.

Any ideas?

Question has been answered here:

https://forums.plex.tv/discussion/190892/playing-a-movie-with-srt-subtitles-as-separate-file-causes-heavy-cpu-usage-and-paus-in-playback