This is really annoying, but a pitfall of programmatic, bilingual learning. A real teacher could give you better nudges in the right direction, although I appreciate the effort for them to even include these hints instead of just marking you as wrong.
On that subject, what I like about Bunpro is the undo, so if you really can’t figure out what it is asking for, you can reveal it and if you definitely knew the grammar (just couldn’t recall for this very specific case) then you can enter the correct answer and move on. I like to share the big offenders with my wife, who is a native speaker of Japanese and I enjoy that she also isn’t sure about many of them.