Gboard doesn't save new words and use my personal dictionary?
I just figured it out while trying all possible Gboard settings. Turns out that "block offensive words" was activated for some reason, and apparently the word "hon" is considered offensive in some places.

I had no idea it was an offensive word, and either way I'd have thought Gboard was clever enough not to block english offensive words when I'm in "swedish mode" (i.e. when the last word i typed was in swedish and all the suggestions it comes up with are in swedish). Turns out it doesn't care, and "hon" gets blocked either way.