I met this terrible problem in the single mission Pathfinder, the mission failed because the time's out, that's because I spent more than half of mission time to wait for the AI driving the M2 to follow me!
Then I did an experiment in Editor. I drived an armored or a car, and let some or an AI driving some vehicles to follow me in the map DESERT, no rock, no house, not any barriers, I drove straight in full speed, you know what? The AIs were lost!
I found that they had really weird paths, what's wrong with them? They could follow me straight but they turned, Why?