Continuity mistake: When Patrizia paints her phone number on the scooter's windshield the numbers change between shots, check the 5 for example.
Continuity mistake: When Roman arrives at the farm, Letty lowers her gun. From the angle from behind her arms are very obviously lowered. However, when the shot changes to a front angle her arms are raised, and she's lowering them again.
Factual error: The girl in Ed Warren's hospital room is wearing a UConn sweater with the wordmark from their 2013 logo rebrand that had not existed anywhere near 1981. (00:21:30)
Revealing mistake: When Angela walks on the lawn to meet her husband, she clips through the shadow of the CGI billboard behind. (00:06:39)
Factual error: There is a calendar in a scene towards the end of the movie which shows the date as Wednesday April 30, 2021 but the calendar does not align to the days of a real calendar. That date will be a Friday. (01:25:54)