Other mistake: Miles explains the presence of the white bracelets that the Efficient Man slapped on their wrists as biorhythm monitors that act as keys for their room, each assigned to a chakra. Blanc's presence was not expected or announced, but not only Ethan Hawke had an unexplained spare bracelet, but he is also assigned a room, when there are 7 chakras and he brings the guest count to 8. It should also be noted that supposedly they are the "key" to each room, and yet Andi comes and goes from them as it pleases her (ironically the very sort of mistake that birthed the term "Fridge logic") and nobody wears them for the rest of the movie at all because the gag ran its course.
Other mistake: When the four 'Disruptors' that stayed buddies solve all the puzzles, they retrieve the invitation from an intricate miniature Glass Onion at the center of the box. When we see the mysterious outcast break the box open, she gets the card from a compartment on the side. While we are not privy to the inner workings of the mechanism, that's obviously not where it was supposed to be. (00:11:00)
Other mistake: The way Helen and Blanc clash into each other during the blackout differs radically between the first time and the lengthy flashback; in the flashback she is calling his name, and he tells her "There's great danger." Neither happened the first time we saw the scene. (01:07:00 - 01:43:20)
Other mistake: When Blanc points at the fax machine in the mansion, it is printing its journal. The dates shown are from September and October, while the movie takes place in May. (00:30:55)
Other mistake: Claire Debella reacts to the biorhythm bracelet buzzing at her wrist. You can see that her wristwatch is set at 7 when it's supposed to be early afternoon at most. We can theorize that maybe she did not adjust the time to Greece and her wristwatch is still on Connecticut time, making it 2 pm in Greece, but it still wouldn't be right, since Daniel Craig was checking the time at the beginning of the dock scene and it was 10 am, and the ship sailed for 2 hours. (00:13:20 - 00:23:40)
Other mistake: When Benoit and Andi have their little chat on the beach by the pile of bags, they do it under a stealthy pretense. However, nobody can overhear them, and they have a good reason to exchange a couple of words, while they show later in the movie no fear of being eavesdropped on even in their room and in places like the bathroom or the gym who could very well be bugged or have cameras, as opposed to an open and deserted beach. In a flashback we even see them hanging out at the hotel together, exchanging information that reasonably they needed to sort out back in the States. (00:22:35 - 01:12:45)
Other mistake: In the original version and in the flashback, Benoit Blanc's delivers the lines about the "loaded gun on the table" in a different way and gestures differently throughout it. (01:56:10)
Other mistake: During the first part of the movie, the Mona Lisa shield is triggered by all sorts of acute sound; phone alerts, speaking too loudly. Somehow it is also never released (one wonders how can it detect when the threat is over). At any rate, after the gag has run its course, in the third act the protection is not triggered anymore except when the plot makes it convenient (the lighter). (01:57:40)
Other mistake: In the close-up of the article about Andi's death (the second time we see it, during the denouement, since the first time when Helen sees it the framing is too tight to notice), her full name (Cassandra) is misspelled in the body of the article ("Casandra"). It also mentions her sister Helen; if her identity is so well known and accessible, considering how high profile the trial was, it's borderline insane that nobody would know about her; the media would have been all over her. (01:54:00)
