During the part of the mission where you are cycling the environmental controls to get rid of the psycotropic gas, there is a wall that always seems to manage to trap one of my boffs.
To get there:
1.) Clear the first room of the gas,
2.) Continue to the next room and go up the ramp to the second floor.
3.) It is the wall between the two rooms on this second floor. Not sure when or how they get trapped, but they can't get out. Only way seems to be to allow yourself to be killed and respawn.
I have also had them get stuck in other places, such as the small side rooms in the middle of the ramps.
I have had this happen on Holodeck a few times and just today on Tribble. Doesn't happen every time, though.