This is a similar bug, but opposite of the other one I posted.
In this mission, you have to kidnap Jake McNeil. If you're detected, he runs backwards along his route from where he came.
Instead of capturing the base in the southwest and waiting for him to arrive, I parked my toxic soldiers at the edge of the bridge where McNeil crosses the river by racing there with my APCs and alternating between popping them in and out to pick off the rifleman patrols. I also waited for a titan to go down the road before advancing.
A rifleman is there as well, so he triggers the alarm. McNeil is captured immediately after, so I popped him into an APC to drive him back to the starting point which is also the evacuation point.
At this point, nothing happened. I looked up the mission online to see if I missed something, and I didn't.
What's supposed to happen is the map spawns a subterranean APC after you drive him back, but in this situation, it never spawns. Without that, McNeil can't enter it, so the map gets stuck.
EDIT: I've replayed the map and picked off the rifleman so the alarm never rings, but the subterranean APC still doesn't spawn. I'm guessing its spawn is linked to the base getting captured because the first mission objective is still announced even after kidnapping McNeil.
EDIT2: OK... so before, I loaded McNeil with the toxic soldiers into the same APC. This time, I still loaded them all together, but I unloaded it while on top of the beacon before moving the APC and soldiers out while McNeil remained. When they moved far enough away (about 3-5 APC distances), the subterranean APC spawned.