In vanilla Minecraft, Piglin Brutes are allowed to spawn in mid-air because they only spawn when generated. This is due to them not having spawning restrictions registered in net.minecraft.entity.SpawnRestriction. But when piglinsSpawningInBastions is true, Piglin Brutes spawn in midair if the bastion is destroyed.

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This needs to be fixed on the vanilla side, cause now spawns can be added via datapacks, so it should be handled properly in vanilla.