I'm talking about the permanent sidequest given by the Elemental Slave starting perk. Rather than spawning Elemental Slavers once on a level, it seems to keep respawning them periodically, with a cooldown that can't exactly be called long. Going back and forth between levels, I fought them in the same spot about 5 times. As far as I know, the enemies spawned by these kind of quests should appear once per level, or at least, that's my experience with the Hogtied! and Wolf Trainee starts. Whether intentional or not, the unlimited respawns these enemies get makes the perk extremely tedious, and even more so because of the AoE spam that Earth, Ice, and Water Elementals are capable of.