I'm really confused as to why they do this: there must be hundreds of people and hundreds of millions of $s working on the YouTube algo. I'm seemingly in the minority that thinks it's largely brilliant, it regularly uncovers things that are related to stuff that I'm interested in but new takes on them, and sometimes throws up some absolute genius recommendation from nowhere. However, like you, my "Up Next" selection is plagued by videos I've previously watched! It's horrible UX.