Hmmm... I'm at a loss as to how that would happen unless the the tracks in the playlists were inadvertantly deleted from the library. I assume they still exist on the flac disk drive. Maybe restore a backup from a date sometime before they disappeared?
Off topic, but my favorite drummers are Dave Weckl (Jazz) and Ian Paice (Rock). I'm a drummer too, but at 67 my chops are fading a bit. Need to practice more, but I'd rather just play.