The following are present in Mortal Empires and the Vortex:
Major Vampire coast factions do not recruit more than one army when under AI control. If this is intended for them you might consider including a mention of it in their diplomacy screen profile (like how High Elves have "Diplomatic" etc).
When the main legendary lord of an AI Vampire Coast faction is wounded, the faction won't re-recruit said lord until the replacement lord and their army are destroyed.
Followers of Nagash faction can't upgrade their Grave Hill special buildings under AI control and thus can't recruit Hexwraiths.
(issues present with no mods etc)