Vanishing Closed Captions

Using TVHeadend in my media server with Hauppauge 2250 cards.

When I had Kodi v18 then sometimes the captions did not appear, but mostly they were visible.
With v19 captions were visible about half of times.
Now I run v21 and I see captions very seldom.

Yesterday I was watching a channel and captions were working, I hit the record button and recorded the stream. Now playing the stream back and captions do not appear, although I can toggle subtitles off and on, Kodi is not complaining. Then I loaded the TS file into Handbrake and recoded about 10 minutes of it. The resulting MKV file has proper subtitles from TS. Then I tried to play back the TS with MPV and it also does not display captions! 

Now you may say it is not a Kodi problem … but what is it? I’m running Gentoo, something missing in my system? But why I see these captions sometimes then?

Any ideas that might shed some light on this mystery are welcome.