The Night of the Janus - S4-E18
Continuity mistake: In the first boxcar scene, the train is shown standing among brown dirt and dead brush with the trees far off in the distant. When West opens the door to leave, there is a tree right in front of the door.
The Night of the Janus - S4-E18
Revealing mistake: About half way through this episode, the hooded man West is chasing goes through double doors and closes them. West slams his body to open the doors. He steps back to ram his body into the doors again to force them open. Before he does, we see the doors sort of slightly move back and forth (this looks very odd and unnatural) before West slams them open.