The first use of the dash grants invis, if you’re constantly dashing, it does not refresh the invis every time you dash, but only after the first invis has run out (i.e. the invises don’t overlap)
I’ve been caught by the same “phenomenon” myself multiple times, and it sucks every time. I really wish it would just refresh/reset the invis buff every time the dash is used. But this is probably a design choice. One I don’t agree with, but hey I’m not a designer over at fatshark. (or it might be a bug, who knows)
Other than that there’s still several enemies that follow you with their attacks if they’ve started an attack sequence, even if you’re invisible, sadly… such as shieldvermin in their combo, or plague monks/berserkers in their attack combos, to name a few. This part of it is definitely a bug, though.