Especially when returning after a long break, if I answer as well as I can and get the “this would work, but actually we’re looking for something else…” kind of hint, it’s super-discouraging. At first, I’m just thrilled that I got something decently workable! But then I can’t move on without intentionally making the answer worse (because I simply don’t remember what alternative you’re fishing for).
It’s similarly frustrating that there’s no “OK, I really have no clue” button right from the initial question prompt. In the rare cases when I have no memory of the corresponding expression at all, then I have to generate nonsense to proceed. (Again, this affects me especially now, coming back after some time away. Maybe I deserve some pain, but also BunPro might want to more gently re-engage folks in my situation…)
In either case, some kind of direct button for “Mark this as not known” would feel so much better than having to make up a bad answer in order to get told I’m WRONG (No surprise!) and then get shown what BunPro was looking for.