I also had to fight battles that lasted 1,000+ turns, and there were at least a dozen such battles – I didn't notice any change in the AI's behavior after 500 rounds. Was it supposed to change?
Moreover, if the behavior had changed, some of the battles would have ended in my defeat.

I read posts from players in offline tournaments, stating that after prolonged battles, a "desynchronization" can occur. Moreover, this does not depend on the destruction of stacks.

I posted a recording of a battle between pikemen and swordsmen. I tried to kill them with one pikeman without using the "Bless" spell, but after 7 rounds, "desynchronization" begins, even with the repetition of the same actions. Moreover, "desynchronization" occurs regardless of whether we attack with the pikeman or not, or with what RNG we play (fixed or not). In general, the battle plan was ruined:mad:

I suspect that "desynchronization" depends on the complexity of creature movement, i.e., it is clear that they will not "desynchronize" if they move in a straight line and nothing interferes with them, but when they go around obstacles and bypass each other, then surprises may occur.