Continuity mistake: During his conversation with the director, while discussing his costuming, Dalton's hair changes from messy and curled to gelled up and straight.
Continuity mistake: During the interview, while sitting, his striped pants are unzipped for a few cuts, then they are zipped in later shots.
Character mistake: Selena Gomez drives into town in a fully restored 1967 Pontiac Le Mans, which is a long box shaped car. However, when confronted with Bill Murray and Adam Driver, Adam Driver complements her on her 1968 Pontiac Le Mans, which is a completely redesigned shorter curved body style. The two look nothing alike.
Plot hole: The killer shows up at the scheduled appointment at 8 AM. They kill the idiot blackmailer with an overdose of morphine. Remember, that morphine that supposedly killed Thrombey in 10 minutes. Marta finds the blackmailer at 10 AM...alive, and does CPR on them, keeping them alive long enough for the ambulance to come and bring them to the hospital, even if in critical condition. So we went from "kills in 10 minutes, you can't even try to save him" to "after 2 hours, you are still hanging on"? (01:56:10)
Continuity mistake: When Peter and MJ hug on Tower Bridge he gets some blood from his face onto the left shoulder of her jacket. From other angles there's no blood.
Continuity mistake: After Mick Mars has Nikki and Tommy kick the guy out with the guitar at his audition, the guy leaves and cries through the door. Nikki is standing by the door and looking nearly straight forward as the guy leaves, but then the camera changes angles and suddenly he's looking more to the side towards the door. Also his arms are a little higher up holding his guitar.
Factual error: The film is set in 1987 but most of the street lights seen throughout the movie are LED street lights and some high pressure sodium Philips lanterns (produced from the early 1990s to early 2000s), neither of which were around back then. Similarly many of the shots of the M1 motorway show modern cars and smart motorway/variable speed limits, which never existed at the time.
Other mistake: Vic and Stu get into a shoot out inside the animal hospital with some thugs, guns firing all over the place. The building is full of animals like dogs and cats and parrots. However, the animals stay completely calm and quiet during the entire gun fight and seem unaffected by the rapid, very loud banging of gun fire. Even right after it, a cat that just had it's tail stepped on sits on a dead body and meows like nothing happened. This is completely uncharacteristic of how animals would act to loud gunfire in an enclosed building, especially in a vet's. (00:45:00)
Plot hole: Spoiler. Agent M points out as highly suspicious that the twin assassins knew the location of Vungus, and High T backs her up on this, saying that only a handful of MIB officers could have leaked that information. High T also established that those aliens were part of the Hive collective. It turned out that they were not part of the Hive, and the Hive connection was made-up entirely by the villain himself...which is the Hive! What he did was absurdly counterproductive to his cause: nothing except the report he himself made up connected the Hive at all with the case.
Continuity mistake: When Anna's singing "The next right thing" she puts a bag on her shoulder, with the strap on top of her hair. After the camera spins round her, her hair is suddenly on top of the strap. This bears a strong similarity to the mistake in the original Frozen where Elsa's hair passes through her shoulder - might be a deliberate nod, or else animating hair around objects is difficult enough that shortcuts are often taken.