(at around 1h 18 mins) When Bill decides to buy back his old bike, he is talking to the seller (Stephen King) for quite some time. If you pay attention, you can see that the book on the counter has been rotated several times between the cuts.
(at around 2h 35 mins) When the older losers look in the window and see their younger selves, the scene flashes back to the younger versions talking after defeating IT. Eddie is still covered in vomit but Stanley doesn't have the wounds on his face from being bitten by Judith.
Beverly is kidnapped by Pennywise towards the end of the first It (2017), prompting the other boys to go to Neibolt to save her. In the flashback to the aftermath in this movie, Beverly is on her bike. She wouldn't have had her bike if she'd been kidnapped by Pennywise.
At the 2:00:45 mark, as they are crawling through the water the bandage on Eddies face appears on his right cheek as he crawls toward the camera when he was injured on his left cheek.
(at around 2h 40 mins) At the end of the movie when Bill and Mike are talking on the phone. Bill takes off his reading glasses twice. Once in the first shot and again in the second.
(at around 1h 13 mins) When Richie is playing the original Street Fighter (1987) arcade game against another boy, the onscreen image is from the game's single-player mode.
The phone number on caller ID when Mike calls the group is not an American number. The area code for Maine is 207, but no American prefix begins with 0 or 1. This is meant to indicate a fictional phone number, similar to the "555" phone numbers commonly seen in movies and TV shows.
(at around 2h) When they enter the sewer, Eddie's bandage briefly switches from his left cheek to his right. Also, Beverly's flashlight is in her right hand; in the next shot it's in her left. (Flipped negative)
(at around 2h 5 mins) Despite Ben and Bev's tokens being made of paper, and despite the characters being completely submerged in sewer water, the tokens are then shown to be completely dry.
When Pennywise hits his head against the glass in the room full of mirrors, it clear that this was easy to break glass.To protect the actor in the Pennywise costume from getting hurt and the actor playing the kid from also getting hurt. It breaks to easy, and would take a lot more strength then depicted on screen.
How are Beverly and Ben able to find Richie's glasses so quickly??? The water is clearly murky and anybody who has went swimming in a lake would know how hard something like that is to find. Clearly they had a mark or the director was telling them were they fell, behind the camera.
In It chapter one after Bill and Richie fight, Richie shoves into Bill's shoulder when walking past him. In the flashback of this scene in It chapter two, he just walks away.
When Beverly is having a flashback of talking with her dad at the table, you can see Big Mouth Billy Bass on the wall. In 1989, this would not exist as it was invented in 1998.
(at around 1h 27 mins) When Adult Ben has a flashback of a instance where Pennywise, shape shifted into a form of a Beverly with hair literally on fire and her face melting off, chases him down the school hallway reciting the poem he wrote to her. He misquotes a line of the poem, saying "February embers" when in actually it is "January embers". It is simply mimicking Beverly and is trying to scare young Ben, so it is entirely possible that it would miss a line or two, so this could be intentional, as it is copying Beverly and It isn't Beverly.
During a flashback to summer of 1989, arcade cabinets of Mortal Kombat (1992) and Mortal Kombat II (1993), both '90s games, are seen at the movie theater.
(at around 58 mins) When the young Losers Club are in their clubhouse, a modern can of Shasta Cola can be seen in the background. An era-appropriate Shasta can would have had block lettering.
In a couple of flashback scenes, a young Ben Hanscom in 1989 wears a light blue t-shirt with horses on it from The Mountain. Actually, this t-shirt was from 2004.
Richie's Mustang is the MY18 model and not the MY16 model.
(at around 12 mins) The New York City street that the car is driving down is actually a street in Toronto Canada. A dead giveaway is that the car passes by a Rogers storefront, which is a Canadian business. Also, the Cafe Landwer restaurant (seen twice in the scene) is located at 165 University Avenue in Toronto, Ontario, Canada.
(at around 2h 40 mins) After the climax, the camera pans over the town and you see the sign "Royal LePage" on one of the buildings. Royal Lepage is a Canadian real estate owner-operator that doesn't exist in the US, so you know it wasn't filmed in Maine.
(at around 57 mins) In the clubhouse, Richie reminisces about how Pennywise "would do that little dance", mimicking the dance Pennywise does for Beverly from the first film, when Beverly was the only one who witnessed this.
First contact is made after 27 years but somehow they know the numbers to call on their mobile phones. Mike clearly has some kind of link with the losers, and could have got this from this link. It's just not explained very well, and is more evident in the book.
What happens to Eddie's body after he dies??? After the losers destroy Pennywises lair, It is never explained if the police or other public figures ever find his body, and his body is just left there. Eddie had a wife and they would have wanted her to know, but it's never explained in the film if she was even told and his body was just ignored.
(at around 1h 50 mins) When Richie tries to remember what he said during the Losers' previous battle with Pennywise, He asks Bill if it was "Let's kill this f****** clown" and Bill nods. Actually what he said back then was "now I'm gonna have to kill this f****** clown".
Why does Richie Wear his glasses when jumping into a lake??? Richie should know that he could lose his glasses in water. It just something when you wear glasses you don't do. **People who wear glasses are only human-they sometimes forget to take them off, or they lose them, etc. Richie has recently experienced fear and grief, and likely isn't in a rational state of mind.**
Richie is seen multiple times not wearing his glasses, either because they didn't want the Camara to reflect or the actor was uncomfortable wearing them. He clearly doesn't wear contacts, so this is a mistake. **People do take their glasses off once in a while-they aren't glued to their faces.**