I was playing through calamity with FMM installed and whenever I killed the WoF my world would crash. The function it crashed at was a rendering script for Calamity that had to do with rendering NPCs. I went through mods and disabled them to figure out what was causing this. After disabling FMM and killing WoF the world successfully went into hardmode with no crashes. Wanted to report this here so the devs can work on a fix.