Ben receives a blue string on his right wrist from Kristen earlier in the show to help with his night terrors. Later, while Ben is on his computer looking at articles, the blue string is on his right wrist. After he wakes from his night terror, the blue string is on his left wrist.
When Sheryl holds the dollar bill out toward the candle, the back is seen, upside-down; when the shot is reversed, and the bill is burning, it is right-side up. This happens twice, showing the two different takes being spliced together.
When Kristen coaches Lexis about the upcoming police questions regarding her alibi for the murder of LeRoux, the child brings up that Ben installed the alarm system that day so Kristen could not have left without setting off the alarm. Kristen agrees. However, an alarm system that went off whenever the residents left their residence would make no sense. That is why these systems can be deactivated by the owners, and activated from outside or via timers.
The sigils on the demonic "map" are perfectly round. Since the original map in the Vatican codex was photographed in a rush, freehand, at an angle, they should appear ellipsoid from the perspective distortion.
Kristen tries to coach her daughter Lexis for the police questions about her mom's alibi on the day that she murdered LeRoux. It makes no sense for Lexis to even remember what day that was because nothing related to the murder stood out to her that day. After all, she only ever learned about the murder days if not weeks later. Normal everyday life is a blurr to normal adults, never mind children.