I guess you're not willing to try 'Remux into file'.
I am in the USA and got full-length subtitles in shows, with 'Remux into file'.
Using 'Extract to SRT file' gave me the same result as you, they cut off.
If that ever gets fixed, it may be a long wait.
Stan001
Back when I first started getting into this...hobby...I was remuxing everything into the original file, back before I knew about external subtitle files. Then when I noticed some captions were not showing at all (or were showing with weird characters), I started becoming more of a control freak, and started using software to edit external subtitle files as-needed.
Most of the streaming services SF has modules for handles the external subtitles just fine. The only ones I have a problem with (for the USA) are Pluto and Tubi (the latter having the occasional glitch of having the end of the file corrupted, which can be fixed but it's extra work I'd like to not have to do at some point).
Given that I'm sure there's still bigger fish to fry, I don't want to push the issue. If I'm deperate there are sites I can go to to get them, but as the files I get from those sites are lower-quality compared to the "premium" sites, my attention right now is on those "premium" sites.