Character mistake: Sam tells Mindy at Martha's, "Come on, it's just a movie", in response to her idea the killers are Stab fanatics making a "requel". In diegesis terms, it makes no sense that Sam questions this motive: Dewey states in a previous scene to her, "Your killer's obsessed with the Stab movies, right?" Contextually, she is Billy's daughter, knows his motive was based on horror film obsession; her would-be schoolmate at Woodsboro High (2 grades above), Charlie (Scream 4), was also a Stab fanatic killer. (00:41:00)
Other mistake: The Reporter states it has been 25 years "almost to the day" since Billy and Stu died (1996), making it September 2021. Tara is a high school senior, and her older sister, Sam, Billy's daughter, is stated multiple times as 5 years older, 23 at best. Many Easter eggs on Richie's laptop state STAB 8 is a 2021 release, which was "last year" according to Sam and Mindy in separate scenes, making the film set 2022, 26 years ago. Sam is 1-2 years younger than she should be, or Tara is 20. (00:57:14 - 01:47:18)
Plot hole: Samantha has watched Stab, knows her father's story, and yet does not recognize she is entering Stu Macher's house. The cancelled Stab 3: Return to Woodsboro, seen in Scream 3, confirms Stu's house exterior looks exactly the same from the original Stab, and is being re-used as a prop for that film. (00:01:26)
Continuity mistake: After the sheriff is killed Sam and Dewey leave to go to the hospital and it's daylight. On their drive to the hospital it's dark out. Then when they take Dewey's body out of the hospital and Gayle shows up it's suddenly light again.
Continuity mistake: When Sam is assaulted at the hospital the first time, Ghostface misses Sam with his knife, which gets stuck on a poster on the board. By mistake, he 'stabbed' the third column of the text on the poster, but then the knife is stuck in the first column instead, then he pulls him out from the third column again, resulting in a hole in the second column. (00:23:55)