Continuity mistake: When the Senator is about to be sacrificed, the cloth on her mouth immediately disappears for a split second. (01:29:35)
Continuity mistake: He cuts a hole in her pants for insemination. When in the car moments before fighting the dog there is no hole.
Continuity mistake: It was briefly stated in the second film that the T-Virus was created by Dr. Ashford to cure his daughter Angela and that the Red and White Queens were based on her. This movie contradicts that by suggesting that Dr. Marcus created the T-Virus to cure his daughter Alicia, and that the Red/White Queens were modeled after her. While the rest of the movie stays true to the continuity of the previous films, this rather obvious ret-con is still a major continuity gaff.
Factual error: The school sign, supposedly in the 70s, is showing an 11 digit telephone number with an area code starting with 012. The 01 prefix was not implemented until 1995.
Continuity mistake: When Maddie is coming up with an ending to her novel, she opens one of the ending drafts. Not long after opening the draft, she decides to go on facetime and make a call, whilst the draft is still open, then the man she is trying to contact calls her back. She then closes the laptop and tidies up. When she returns and opens up the laptop, the draft that was just shown on the laptop has become a completely different one. (00:10:10 - 00:14:25)
Continuity mistake: When the passengers are first boarding the train, just as a couple ask the female train attendant where Car 4 is, two women can be seen boarding the train behind the attendant. The attendant then points to Car 4 and a man with a suit and backpack has suddenly appeared alongside the two women. (00:13:05)
Continuity mistake: While Eddie performs "Hot Patootie", he's seated on the motorcycle with Columbia for a bit, and when Eddie stands up he's holding the mic in his left hand, but as he walks up the steps it's in his right hand, then next shot when he's facing Frank-N-Furter the mic is in Eddie's left hand, and next shot it's back to his right hand again.
Continuity mistake: Throughout the movie, fire axes seem to be the weapons of choice. Only two fire axes are used, but they appear recurrently. In the very first use, the protagonists use fire axes to butcher the monster Beverly. Blood and gore go everywhere; yet, the axes emerge from this bloodbath with no blood or gore on the handles - they're virtually pristine moments later. The axes are used again and again, right up to the ending, and blood comes and goes from the axe handles seemingly at random.