In theory there are unbeatable levels. With some updates Nintendo fixed glitches, hit boxes, etc. Usually, when you play a level that was uploaded on an older version of the game, you get the old behavior. But there was one update, which did not adhere to this, and which did cause some levels (designed with now fixed glitches) to be unbeatable now.
But this project isn’t about beating all levels, it’s about beating all uncleared levels. Since those glitch levels probably were beaten before the patch OR you might be able to play them on an older version of the game (if the server allows it), these shouldn’t be a huge problem.