Another common situation is that a question is actually answered by a comment while no other answer is given. So such questions are shown as unanswered (and distract people trying to answer actually unanswered questions). A polite question to turn such comments into answers (e.g., "@[name] Thank you for your great comment! It seems this actually answers the question, but is not declared as such. Would you mind writing the content of your comment as an answer?") might be something to add to the list.