Here is what I've done to replicate this problem. I don't know how many of these steps are important.
I created two courses, both blank "test bed" courses.
I created a new category and a single MC question inside the question bank. This category and question are at the category level (so they could be shared across many courses).
I created a quiz in one of my blank courses. I left all of the settings in the quiz as defaults, including "How questions behave" as "Deferred feedback."
I added my single MC question to this quiz.
I went into my second blank course and attempted to import only the quiz I just created from my first blank course.
I got the "error_question_hint_missing_in_db" error at that point.
I think this is especially interesting because Question Hints are thoroughly optional. 99.5% of my questions do not have hints in them, and the quiz activity is perfectly fine with having things in the hint blocks or not. While the import function is somehow looking for hints as a required element?
Anyway, I will be glad to put in a bug report if someone will verify that this is breaking for them in the same way.
(PS -- As I said earlier, I think, I went through the whole creation of the Question Sharer role in order to have this category level question bank ability, so if you haven't done this, maybe this whole thing doesn't break in the same way?)