Hmm...
The 'counter' for the assignas/movein command is the unassignvehicle command... you could try that.
However a TRANSPORT UNLOAD waypoint should do the same thing. Just note, when using a TRANSPORT UNLOAD waypoint, there's no need for a GET OUT waypoint, or any syncing. A TRANSPORT UNLOAD waypoint should automatically kick all cargo out of the vehicle, no matter what/where the cargo's next waypoint is.
However if that doesn't work, I'd suggest something like:
"unassignvehicle _x" foreach (crew
jeep - [(driver
jeep)])
Which will unassign all the units in the cargo of the jeep.
As for which to use (moveincargo/assignascargo), in this particular case there's not a lot of difference. I'd stick with movein
Try something like that and see if it solves your problem