Two days have passed since the last season finale but Scully's and Reyes's hair is significantly longer.
Kersh refers to King George III as "the King of England". While this is a common error, it is not correct. Kings have Kingdoms. The Kingdom of George III was Great Britain and Ireland. While that includes England, England is not a kingdom. In fact there has not been a King or Queen of England since the Kingdoms of Scotland and England united in 1707 under Queen Anne.
The figure in the shower at Scully's apartment in the beginning of the episode (supposedly Mulder) is wearing dark shorts.
In the clipping of Carl Wormus's death that Agent Reyes finds by the elevator, the word "apparently" is misspelled as "appearantly."
When Agent Doggett is listening to the news report on Carl Wormus as he is getting ready, the reporter says he's in his late 30s, yet the obituary clipping left in the hallway for Agent Reyes has his age as 45.
(19m40s) Reyes is talking to Brad Follmer.
Her face can be seen in the fore-ground, out of focus.
But when she starts saying "not to mention that how excited I was to be in D.C." her lips don't move.