Continuity mistake: When the girl gives Litwak her phone to show him there is a replacement part on eBay, her phones shows that it is connected to WiFi. Litwak doesn't set up his router until later that evening, he has only plugged it in. (00:09:41)
Suggested correction: It's possible she's either connected to wifi at another nearby business, using a public wifi signal, or using a friend's phone as a hotspot.
Continuity mistake: When Kate is hanging on to the sleigh as it takes off she is holding on with one hand. Camera changes and now she is holding on with both.
Continuity mistake: Meg starts the trip wearing a red flannel shirt over a blue cardigan over a gray T-shirt. Along the way she first drops the flannel shirt, then the cardigan (the color of which seemed to have gained saturation). She's not seen carrying them or any bag that might have held them. When she finally faces It, all the clothes are back on. Calvin's case is even more evident: he starts with a jacket over a red shirt, ends up with a just a now-gray T-shirt (matching Meg's) but is back with jacket and red shirt at the end.
Continuity mistake: As Keda is tumbling down the face of the cliff, he smacks against a small ledge on his way down before hitting a second ledge and then landing on a third. But as the camera goes down the face of the cliff from the top of it, the two ledges he hit on the way down are gone, showing a mostly flat face. (00:28:20)
Other mistake: The snow globe from the original is in the loft in the new film, but in the original film, as Mary was leaving the Banks house while they flew a kite, she packed it in to her carpet bag.
Continuity mistake: While Sam puts Slappy on the junk cart the sun changes between shots.
Factual error: The shop owner shows him a tape of the Joshua Tree by U2 and says it is the best concert he has seen, but the Joshua Tree wasn't released until 1987.
Continuity mistake: After Dumbledore gives Newt the card for the safe house in Paris, they teleport to a bridge where they continue talking. Dumbledore then tells Newt why he likes him so much, and in the side shots, Newt is shown holding the card up. When it cuts to angles from behind Dumbledore's shoulders, his arm and hand are much lower with the card and his head turned in a different position. (00:20:35)
Other mistake: The SUV hits a snow embankment. Immediately afterwards, there are no tyre tracks in the snow behind the SUV. (00:31:35)
Continuity mistake: In the opening scene with the skype call, Mia's hair is in front/behind her shoulders depending on the camera angle, with no logic. (00:00:55)
Continuity mistake: Princess Dawn is in her chambers and her servants are preparing her for the coronation. When her book-headed valet tells her "You have come of age", he is suddenly holding the tome with both hands, while he had just one on it before the cut. (00:19:30)
Other mistake: After Kevin and Holly go kayaking in the ocean and get to shore, their upper bodies and hair are dry despite having been in a tandem-style sit-on-top kayak, which generally means the kayakers will get quite wet. (00:03:40)
Continuity mistake: Clara climbs down the cliff with Captain holding her hand. His position changes between shots: He is either leaning over the cliff, or resting aside.
Continuity mistake: When the robber is arrested, his hands are cuffed behind his back. When he's being loaded into the police car, his hands are suddenly cuffed in front of his body.