This is happening on a Samsung Smart TV at my parents' house. I don't own any Samsung TVs and I have never seen this issue so I assume it's a Samsung thing.
All my movies are MKV and HEVC. The files I am having issue with are all from TCM. I'm getting gibberish subs that are black boxes with white letters. I have no control over them through emby as turning off the SRT subs (which are displaying correctly) does not make the problem subs go away so they are on all the time but are random
I can only see these in handbrake, no other tool sees them
They are EIA-608 captions and they're part of the video stream. https://en.wikipedia.org/wiki/EIA-608
Apparently the only way to remove them is to re-encode the video and strip them out.
https://stackoverflow.com/a/51439554
Can you follow these instructions on you TV and make sure Closed Captions are off or disabled in the TV settings Closed captions and other accessibility settings for your Samsung TV