The carriages are not the same throughout the scene. The seat color changes, then the carriage with the black seats is noticeably more ornate than the simple carriage that showcases the actors at the beginning and end of the scene.
In the last 15 minutes of the movie, Priscilla repeatedly kisses Adam while convincing him to marry her. During the first kiss, she leaves a smudge of lipstick above his upper lip. In later kisses, the smudge is missing.
A newspaper article at the end of the movie calls Priscilla Hall a "former fiancé" (male engaged to be married) when it should say "former fiancée" (female).
The first time Adam gets on the elevator at the beginning of the movie the wall behind him is bare. The second time there is a "Hughes Foundation" plaque on the wall behind him.
Wendy and Adam are decorating the "Christmas Future" tree with ornaments that are suppose to have been made by children. Wendy holds up a reindeer ornament to show Adam, but when she turns it back around you can see there is a white sticker on the back with a scan code.
At the theater, Wendy gets on the elevator but walks to the back/center and never presses a floor button. Adam immediately follows and presses the hallway button to open the same elevator, but then he also boards, walks to the back and does not press a floor button either. Charlie then uses his key to stop the elevator, but it would not have been moving without a floor being selected.
Lips of a male singer don't quite match within a chorus singing about figgy pudding.
In the beginning, Priscilla establishes herself as a selfishly inconsiderate and controlling woman, making demands on Wendy's time at all hours via her cell phone, but when she leaves town again, Wendy isn't phoned even once.
It's unexplained why the choral group singing in Priscilla's apartment building (bursting into song when elevator doors open) appears later in the Christmas-tree lot. It is also not explained how they--full of the Christmas spirit--shove their way unthinkingly and rudely into the elevator (while singing), trapping Adam, who is obviously trying to follow Wendy out.