Continuity mistake: Peter is in Lara Jean's kitchen, wearing a jacket. Her dad comes home, he and Peter shake hands, and in one brief shot Peter is not wearing a jacket but a plain short sleeve top. Angle changes again and the jacket is back. (00:39:00 - 00:40:15)
Continuity mistake: When Ana and Christian are having sex on the dining room table, she drops Christian's pants below his butt. Scene cuts and Christian's back is shown, with his pants above his butt. Then cuts back and they're below again. (00:54:40 - 00:56:50)
Factual error: In the second last scene, when Rachel is leaving Singapore for New York, Nick went onboard to propose, and convinced her to stay in Singapore for one more night. However, that's not possible in Singapore as there are strict laws stating that those that enter the departure area must have a boarding pass, with the purpose of leaving the country. Those that have a boarding pass but have no intention to depart the country will be prosecuted, and in 2018 40 people were arrested for various reasons, such as sending a friend off and meeting their idols, etc.
Suggested correction: Nick's family is extremely rich, powerful and famous in Singapore. That might have been enough to get him special treatment or an exception to the rule.
Other mistake: When Kate is taking the Medical-Surgical Nursing Exam, there are 2 separate #23 questions at the bottom of the page. (01:09:30)
Continuity mistake: When Buster is shot, his hat with the hole in it disappears.
Factual error: The plane used in the film to take Juliet back to London towards the end of the film is a replica of a Dakota C-47. She is painted with black and white "invasion stripes" on both the upper and lower surfaces of the wings - approved in May these were only widely put into use for D-Day in June 1944. After one month the upper surface stripes were ordered removed, and by the end of 1944 they were ordered completely removed. By 1946 when the film is set they would have been long gone from any serving aircraft still flying.
Character mistake: The tour guide inside the "Degenerate art" exhibition ridicules the 'child-like' paintings of the likes of Mondrian and Kandinsky. In particular he stands in front of Kandinsky "Upward." The German name of the work is "Empor", but the tag says "Empore." (00:03:40)
Continuity mistake: Danica gets to work at the beginning of the movie, and her coworker passes her a folder. The folder keeps moving from under her arm to her hand, back and forth between shots. (00:03:00)
Continuity mistake: When Willy is in bed looking at photos with the camera behind his ear, his cup of coffee is directly in front of his hands. A moment later when the camera shifts to in front of him, his coffee is way off to his side, nowhere near his line of sight. (01:00:12)
Continuity mistake: When Rick and Kirsten are at the game, just after they shout at one of the players, Kirsten drinks from her cup, but in the next shot, the cup is suddenly back in the armrest holster. (00:33:40)
Continuity mistake: In Alice's apartment the clock on the wall has the time as 8:40 when she is standing and kissing David. They have sex and Veronica comes over. Alice and Veronica talk and the clock still shows 8:40. (01:20:00)
Continuity mistake: After performing 'surgery' on the bear, Tasha goes visit another one of her little patients. Before she sets foot in the room bickering with Jeff you can see her hair flows left and right of her colourful pin on the coat. Inside the room, her hair is just on one side, switches side, and it stays that way till she exits the room, when once more there is a visible change at the cut. (00:03:30)
Continuity mistake: Kevin and his daughter handed the invite for the dream-like contest to the protagonist. He shoos her away saying "Liv, don't you need some milk with that cookie?" His arms are crossed behind his back. Next shot and she is walking away from him with his hands crossed in front of his crotch. (00:02:20)
Continuity mistake: Abby's annoying boss puts her friend to work giving him a box to carry to his car. In a rather blatant continuity mistake, the penguin is facing opposite directions between shots. (00:03:15)
Continuity mistake: Violet's mom is hot combing her hair at 5 AM; as she performs this operation on the left side, the right side has straight black hair all in front of the shoulder. When Violet tells her that dad is coming, she moves to the right side. Sanaa Lathan's hair now is suddenly all behind the shoulder. (00:05:20)