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I recently had to remove My Thumbs Up and Avenged Sevenfold Radio Playlist, as keeping track of them has become a bit of a nuisance for me.
For My Thumbs Up, duplicate songs tend to show up as you "thumbs up" the same song on different stations. Also, tracks will sometimes be replaced with similarly titled tracks - which are sometimes a different version, an inferior quality, or sometimes an entirely different song.
Two of the things I would suggest is avoid duplicate tracks, and to not replace certain tracks. I like to organize my playlists, which means that I manually put the tracks in alphabetical order.