Indeed, it does appear to be terrain based. The centre room of the Temple of Anubis (with the seven doors branching off it, y'all know the one) is mostly impervious to AoE spells. The delay on Fireball application didn't actually fix it, as you will still encounter mobs which do not care about AoE spells.
The real shame here is that Akiri dungeons are one of the only places evokers should get to have fun, but their spells won't work... tragedy.