House of Lancaster AI :
Never builds the maximum number of Manors. Generally, the AI builds a limited number of Manors, ranging from 5 to 8 maximum, although the maximum limit is 11.
All AI:
After the latest update, AI Hardest difficulty and above (Ridiculous, Outrageous, and Absurd) builds far fewer military production buildings than before. Basically, one siege workshop and maybe two or three barracks/stables/shooting ranges. However, this isn’t enough to replenish its troops after losses in the late game, so even with a lot of resources, the AI simply loses due to a lack of troops.