Revealing mistake: In the final scene when Annie and Sam are exiting the observation deck coming towards the elevators, the New York skyline backdrop which should be visible behind them is missing, and the entire sound stage wall can be seen beyond the observation deck safety railings instead. 'Although the exterior and lobby of the Empire State Building, 350 Fifth Avenue at 34th Street, are the real thing, a slightly larger replica of the Observation Deck was built in a hangar at Sand Point Naval Base on Puget Sound just northeast of - where else? - Seattle.' https://www.movie-locations.com/movies/s/Sleepless-In-Seattle.php. (01:39:35)
Visible crew/equipment: After Phil drives the truck off the cliff, and it explodes in a burst of flames, there is a shot of Andie MacDowell and Chris Elliot staring in shock at the disaster. The two actors are bathed in an orange glow supposedly coming from the flaming wreckage. But in the lens of the TV camera Elliot is holding, there is a noticeable reflection of the lighting equipment used to create the glow effect on the actors. (01:04:15)
Continuity mistake: At the beginning, when Rochefort walks out onto the balcony to address the Musketeers in the courtyard, the guard on Rochefort's left obviously changes halberd/pikes between shots as they are completely different. (00:08:20)
Continuity mistake: In the hotel scene where Gavin is murdered, after speaking w/Darby, he eats one of the chocolates on his pillow next to the night stand. He leaves the chocolates and the Westin card on the pillow/bed. Then when they show a shot of Gavin sitting on the bed brushing his teeth while Khamel hides in the closet waiting to murder him, the chocolates and the card are gone. Then, after Khamel murders Gavin, the chocolates and the card reappear back on the pillow as Khamel walks over and eats one. (00:59:55)
Continuity mistake: When Arnie is playing with the grasshopper in the letter box, the way he grabs the insect changes between a shot and another one.
Continuity mistake: When the crime bosses meet up at the casino, in the exterior shot, there are a few items on the desk including a bottle, an ash tray, a plate with a slice of pizza and a newspaper. Later, when Batman appears and punches one of the crime bosses onto the table, the bottle, ash tray and plate have suddenly moved closer to the newspaper. (00:02:00 - 00:02:28)