Subtitle makes video stutter

I have a movie downloaded that is 2160p hdr. The movie plays fine on apple tv 4k but when they start talking and the subtitles appears then I experience some stuttering issues. I use a macbook pro early 2015. Plz help

Would you be able to send in a small sample we could test here?

Samples can be created with http://www.emmgunn.com/mkvtools-home/ and submitted at http://firecore.com/upload

I just uploaded a sample to the link you sent me, good luck and thank you.