So, for some reason, maybe because the title is so short, Stephen King's It is on listchallenges as separate entries a ton of times. Feels like every time I see it on a list, its a new entry.
Its impossible to list everything, I'm sure. Finding the "wrong" entries is hard, since the search isn't geared to it. I've done my best to be as complete as possible.
If I had to guess about the second most common title, I would say its probably Avengers Endgame. It has a bunch of entries, but the wrong/new entries don't appear on lists as often as It, since Endgame is easier to search for.