If they originally were in TS containers, I assume that the subtitles are actually ‘closed captions’. And these do require always transcoding in Plex.
There is a way to extract them and convert them into the much more compatible SRT format.
However, this cannot be done directly in Plex. SOLUTION: EIA_608 Subtitles Suck - Here's how to automatically replace them with srt goodness
But maybe I am wrong and these subtitles are from somewhere else.
