its even more so in 1.3 patch. AI seems to have the tendency to declare war on factions that are already fighting on multiple fronts. In my recent save, west empire declared war on battania and valandian, then aseri and stugian joined.
Also, picking enemy seems to be broken too. AI lords sometimes declare war on faction soooo far from their heartland. What you'd expect is that, they gather an army, took a exclave settlement far from their base, that settlement gets attacked later, gather another army travle across the world to defend, in the process an neighboring faction declare war on them, and took settlements easily when no one is there to defend.