After Mike kills Epstein with the hammer the blood spreads on his face and cap. A few shots later when he returns at the cabin, the blood on his cap disappears.
When they go out to the car to shovel it out from the snow storm, the snow is up past the tires, yet, down the driveway tire tracks can still be seen, as if it barely snowed.
When walking out to the shed, Mike has a Sledge hammer in his hand, yet when he delivered the death blow to Epstein it's a claw hammer, not the sledge hammer he took out.
When Mike deals the death blow to Epstein by hitting him in the eye with the claw hammer, the hammer is shown to be lodged in his eye or still in Mike's hand, depending on the camera angle.
When AJ leaves the hot tub and urinates, he is in his underwear and boots. When they drag him away from the hot tub, he clearly has white long johns or sweats on his legs.
When reading the police flyer they said it was from the Truckee County Sheriff Department. Truckee is in Nevada County; there is no Truckee County.
At around 20 minutes into the film, Nichole is accused of texting her boyfriend as the group of friends has received the final instructions to get to Thomas's house. And yet, later none of the cell phones have "bars" or reception to call for help.