I ran across this over the Summer and I forgot to file a bug about until today. When an AppleScript performs delete on a playlist, the playlist is seemingly removed from Music but its name is still displayed in the Sidebar. If you click to select this playlist—that was ostensibly deleted—the view from an adjacent playlist is displayed.
This leads me to believe there's some clean-up or reload that fails to occur. If Music is quit and restarted, the Sidebar of playlists will display as expected; that is, the "ghost" playlist that was deleted will not appear.