I am using the latest beta patch, which i think was meant to fix this, though I may have had a slightly different problem.
In strict Army by Army mode, and AI battle came up, and started getting screwy, first it took ages for the ai to send its units the front, then the unit it sent started 'flipping' with another (from a different army) and then on side got its front ready, but not the other. It didn't freeze as such, i could still click around and open the chat window, its just that the German AI seemed to go for a toilette break or something before it finished fighting AI russia.
This was in 4 player mode btw.
A logical solution if possible might be to have the option to resolve AI battles in the backround without going to the battle screen, and just popping up the results?
Otherwise, the improvement in speed over the last time a played (a while ago) is superb!