I ran into two bugs recently in the AI, and I can provide a save game that covers both at the same time if you wish.

#1. If a sovereign has lost his last city but is still alive, but cannot see anywhere inside the FOW to found a city at, he will stand still instead of explore for a spot.

#2. The Dark gate is a Sovereign Trap.  Late in the game, a custom sovereign is sitting on the Dark Gate quest trigger, unmoving, and all the other AI sovereigns are gathered around him waiting their turn. Turn after Turn they never leave or do anything else. In fact, even the most mortal of enemies refuse to attack each other even though they are standing next to each other.

Single Mindedness on getting to that quest trigger that a single sovereign is hogging.

Hope that helps flesh out the AI bugs.