I have the same issue with the Special Delivery achievement. I tried logging into another Xbox to see if it popped there and rebooting my primary Xbox, but no luck in either case. I finished the mission solo on my first try, so I did not run into the mission glitch that I have seen elsewhere where you would spawn away from the truck.
Hey guys! For achievement issues, we recommend these Xbox steps and this FAQ from Xbox. As previously stated, we do not have the ability to force unlock achievements on accounts. You can also double check that you have completed the necessary steps in the guides here.
Otherwise, you can restart the game or attempt the achievement steps on a second profile. We apologize for any inconvenience.