Piglins are spawning in bastions even on peaceful difficulty. Normally i wouldn't see this as a bug since piglins (if i'm not mistaken) are considered a neutral mob since their hostility towards the player depends on the circumstance, and i'm pretty sure certain neutral mobs can spawn on peaceful (such as Wolves and Iron Golems), except that piglins don't spawn ANYWHERE else in the Nether that they're supposed to, so either Piglins are failing to spawn in their biomes away from generated structures, or they're wrongly spawning in bastions.