When Frank is demonstrating his dance moves to Mac at the club, a waitress is seen passing behind him. It cuts to Mac's reaction for a second, then when it cuts back to Frank the same waitress passes by in the same direction again.
When Dennis's gets out of the car to confront Mac, he is parked next to a flight of red steps; in the next cut the steps are gone.
When Dennis and the Waitress are in the office talking to Charlie, you can clearly see a gap where there is no ceiling.
At 0:18:00 we can see a crew member's muted reflection in the sink/stove.