The two that I wrote down after the first occurrence happened on the mission "Crossing Paths" after meeting the FIA contact and clearing out the first small town, which the soldiers fell into line formation and sat there until I saved and exited the mission.

The second noted occurrence was on "Radio Silence" after securing the radio station and not moving on the repel forces stage.

A simple save and exit, then continuing from the main screen allowed these mission to continue.