The subtitles work smoothly in the background so new videos don't have them at the start but will get them automatically after some time. "Some time" is defined by the amount this background task has to do - so more videos -> slower subtitle generation. Did you spot any videos that do not have subtitles but an actual voice track? Then please let us know in the 3speak discord or here as comment and I will have a look :)
RE: 5 Things About 3Speak You Probably Didn’t Know (Part 1)