In case this happens to be the issue (because it trips up, or at least irks, some seasoned sellers....)

If a buyer sends you a message about an item, and you read / reply to it, and then they respond with something like "thanks", obviously requiring no further reply from you as the seller, eBay will still see that the buyer's last message was not replied to and the system counts it as an item with unanswered question, resulting in you seeing something like "X items have questions awaiting answers" or something similar.

In these cases, I periodically click on that link that reckons I have questions to answer (they'll all have an "unanswered question" flag on them in red), then when eBay loads the list of items with open "questions", I bring up the drop-down menu on the right hand side and select "mark as answered".