Placing a pylon with 160 purity range close to an evil biome crashes the game for me. Something goes wrong when it tries to clear 1500+ blocks. I suspect it might be because of the evil spreading back while clearing, so I just downloaded the Begone, Evil! mod to check if this is the case and will add a comment or edit the post if this fixes it.

EDIT: Begone, Evil! Completely fixed the crashes. It is likely as i suspected, a bug when evil is spreading while the pylon is clearing a large amount of blocks..