Hey !
I played again this scenario with some friends and when we were in the vehicle, going toward our mission, the vehicle bumped into a barrier on the road, turned back and litteraly went in the wrong direction while the camera stayed above the barrier.
Not sure if that case can be corrected ?
Cheers

Edit: The edited version was suggested by Domian Blackwood (24 Dec, 2016 @ 9:55am)
"Here's a quick fix for mission. Drop the misson file in to Arma 3\MPMissions. In game sit to the passanger seat next to driver (Ride in back) and go to the driver position from there. Then drive to the next mission waypoint without intro."
https://drive.google.com/file/d/0B5YKbP_UbR5hSWFPWGJBdFVFMHM/view