Hi,
so, my Philips 55PUS6482 usually shows subtitles without any problems, but with this series it started showing titles in this big black box. Is there anything I can do, on the TV or the subtitle file itself?
Sorry for the blurry photo - https://imgur.com/a/MuQJyyi
I would try another video player. VLC is my go-to, it has support for subtitles as well. If this is the first time your having problems like this with subtitles, and its only with this specific show, then I would assume its the media player's handling of the subtitle file.
What video player are you using?