For a map in which the playtime is several hours, I tested the AI. I noticed that after about 2 hours, the Zerg insane AI sometimes stops attacking at all, and they wont build new units and they harvest ore only. But sometimes they do keep attacking as they should, even if I retest the same map, in the same settings. The Terran AI does not seem to have this problem.

Yeah I've seen this before... This happens a lot when there're either too many units or when it's been a long game... Some Ai glitch or something just stops them from doing anything...

An example would be Crash RPG, if you played the game for a long long time and get to a point where the map creates a few .. let's say.. guardians.. the guardians will not attack... even tho the triggers constantly triggers for the Zerg Insane AI.
This effect can be overrided by using Order - Patrol ..or Random suicide mission (i think)