Hello. I've got the same problem with this mission: after "show of force" convoy didn't start moving.
I have a track of this mission. I can send it to you, if you want.
On the second try everything worked fine. I don't know if this is correct, but the truck didn't drive away. It was standing near the crossroad. Convoy just went near by not paying any attention.
Anyway - awesome campaign! Thank you for it!