Mine work fine
I have the same display and I play movies from my USB drive. What I always do is put the subtitles file (.srt) exactly the same as the movie name. For example the title of the movie will be Avatar.mkv and the sub should be Avatar.srt. You should just copy the name of the movie and replace the existing sub name by it. Lastly both files should be in the same folder. (make sure the .srt is made for the movie i.e same bit-rate etc...).