Plot hole: When Dr. Hughes is racing to save Allison when he thinks he is Carter from the events that happened in "I'll be seeing you" Henry says he is racing for a cliff, and that the cabin was just a hologram. But in the episode the Cliff was the hologram disguising the cabin. Henry even commented in that episode that he did not remember a cliff being there.
Other mistake: When Holly and Fargo are playing Dungeons and Dragons, Holly rolls a d20 die and yells, "Critical hit!" but we can see the 20 on one of the upper sides of the die, meaning that she actually rolled a 2, which is most definitely not a critical hit (and actually nearly a critical miss).