Force press to select a word just doesn’t really work well. I am trying it now in Safari and most of the time the word is selected and the menu pops up and when I release my finger the menu and selection instantly disappear. Other places with force touch actions I’ve found equally buggy.

edit: Oh i played with it a bit more and it seems you have to press gently first, then hard. You can’t press hard straight away or it reinterprets it as a light touch after you let go. That’s quite unintuitive.