Idiot Ball: The White Lotus coup in FISOT 4. For one thing, the stated reason for betraying avatar Aang (Protecting the baby Avatar)means they're betraying the living Aang for the dead one, as their mission to defend the new avatar came from Aang in the source material. The White Lotus' interactions with Aang in the original series clearly show that they felt no obligation to help the avatar then. Furthermore, the leadership of the organization would likely fall to people like Tenzin and the living Aang, who would never launch a coup. Other than that, most of the originally ISOT'd White Lotus members would be pushing sixty, and the rank and file would be made up of various peoples from the new world they're in, who'd have no loyalty to the dead Aang.
Mary Suetopia: A common complaint of how well Ilium is doing in FISOT4. Technologically advanced nation, able to troll everyone else around to, has yet to suffer a single defeat... An awoken Cybermat in their territory is meant to curb this trait, and they suffered a large defeat against the rebels Daleks before that.