Audio problem: As Annie is trying to leave Joan's house and she starts to give Annie instructions on how to do the ritual, it's obvious the audio for Joan's lines was dubbed in in post as a lot of her speech doesn't quite match up with her lips. Especially when she's saying "Your whole family needs to be in the house". (01:08:00)
Factual error: Spoiler: In the scene toward the end of the movie when the dad is burned alive, his skin is completely black but his clothes are still on and intact, just blackened. With fire hot enough to completely blacken the skin, it would have burnt the clothes completely off (or at most they would have been shredded rags). (01:51:25)
Continuity mistake: Peter dives through the window of the attic, shattering it with shards of glass and window frame busting out and falling with him. When the camera pans down to him lying on the ground, there isn't a single shard of glass or piece of frame seen anywhere. (01:56:10)
Continuity mistake: At the dinner scene, just before Peter asks his mother if she's okay, the meat on his plate, (apparently chicken) is sitting with the mounted end up. It cuts to his mother then back to him without him moving, and suddenly the meat has flipped upside down the other way. And it flips around several times through this scene. (00:56:55 - 00:58:00)
Continuity mistake: In the classroom when Peter is being possessed, he slams his face down into his desk twice, splattering blood onto it. After he falls back screaming, the camera changes angles and now his desk is clear of blood. (01:38:25)
Visible crew/equipment: In the last scene when Peter is in the tree house, blue tennis shoes are moving up and down. This is most likely a camera man (or woman) trying to get angles.
Suggested correction: I watched this entire scene three times and couldn't see any blue tennis shoes moving up and down. Most of the shots in the scene are close-ups of Peter's face. If the mistake is valid, then a timecode and/or a picture would be really helpful, as the scene lasts for a couple minutes.
Revealing mistake: Annie hears the sound of scribbling in the distance and follows the sound into Charlie's room. When she enters at 1:26:13, you see Charlie's doodle book on the bed being written in and the pages flipping on their own. If you look to the left of the bed, there are a few visible wires running from the book towards the wall to turn the pages. In the photos, they can be seen towards the bottom of the nightstand. In motion, it's pretty easy to see the wires bouncing around (from 1:26:13 to 1:26:21). (01:26:13)
Other mistake: The opening text crawl stated that Ellen Taper Leigh (Annie's mother) died on April 3rd, 2018. But after the family return home after her funeral, the screen on Annie's laptop is shown at one point, and the date is listed as 10/9/2017. (00:00:25 - 00:06:51)