Could you describe what settings you have in Options > Video > Subtitles & Language?
Also, what is the particular problem? Is it that you're not getting forced subtitles?
Thanks.
Here are my settings
Red October HQ Version 16.0.123
Show subtitle only if selected subtitle language is different from audio language
Default language :English
Default audio language: English
File Format .MKV HD (Ripped BD)
The result is that all subtitles are shown regardless of language. I believe that part of the problem is that the LAV filter does not have forced subtitle checked but I suspect the interface is not communicating with LAV.
If I watch an English language film with English subtitles, presently the film will play showing subtitles which of course I hope you agree it should not. Sorry my reference to 'Forced' subtitles is a little misleading as I discovered later that just standard subtitles is broken.