There are two situations that I've noticed.
First: There are many upvotes on the answer and no upvotes on the question, or more upvotes on answer compared to question. If the answer is useful then why user don't find the question is useful too as s/he was also researching the question to find the answer and
Second: The question is marked as a duplicate of other but that duplicate question sometimes received more upvotes than the main one.
Third: Question has more stars(favorites) than upvote and around 20k view in just a few months.