AI cannot go through certain (open) fence gates.
For example the fence gate at the factory west of Kore in Altis (position 063162). If the gate is open the AI soldiers will try to find an alternative way instead of going directly through the gate. I made a small script to hide the gate (classname is Land_Net_Fence_Gate_F) but that didn't work.
I tested other gates in Altis but the behavior is the same. The only way of getting them going through the gate is ordering them to board a vehicle, but if they are ordered to move to a certain position, or just following you, they always go for the alternative path.