So, I just got to the College of Winterhold, and the librarian asked for some lost book, that happens to be in one of the dungeons that I've already cleared.
I have the book, and I can't drop it because it says it's a quest item, but there's no option for me to give the book to the guy.

On the map it still shows the dungeon where I'm supposed to get it, and if I go there and try to use the clairvoyance spell, the spell goes crazy and points to nowhere.

It's a minor quest so it's not really important, it just bugs me to see the quest there and be unable to complete it.
Any solutions?

Having the same issue. As stated, not a game breaker by any means, but it is mildly annoying.

Though it is a spoiler and no doubt it will be moved to the correct forum, can you tell us the quest name and dungeon name so others can avoid this issue please ?