Molaktula teleported all the way back to it's spawn room in the middle of the fight using it's teleport attack, then the core stones also spawned in the starting room, unreasonably far from the rift.

Molaktula will spawn fragments outside the rift room if he, himself, teleported somewhere else

Molkatula keeps teleprting from the boss arena.

When I fought Molaktula it teleported a far distance from the boss arena. Then it's corestone phases instantley completed.