Revealing mistake: The final scene is filmed in Brant Rock MA, and the weather is blatantly CGI. If you notice almost everyone is bone dry in a supposed driving rain storm. Look especially at the character perched on top of the submarine tower. For contrast note the "pizza delivery" scene where it is raining heavily and everyone involved is soaking wet.
Revealing mistake: Fight in the toilet of the Paris nightclub: the presumed Lark rips out the sink's drain and begins assaulting Tom Cruise with it; Walker intervenes holding him, but the nimble Asian does a flip and brutally tosses him to the ground. As Henry Cavill is bent over before being snapped to the floor, on his back, you can definitely see a protective pad through the jacket. (00:31:52)
Revealing mistake: During the police chase with Gabriel on his motorcycle, he stops and turns to start shooting at one of the cops. By appearances, Gabriel is using a standard Glock which had a magazine capacity of 15 rounds. He has no extensions on it at all with the handle and magazine visible. Yet he proceeds to fire the gun 33-35 times at the cop car without reloading and in continuous fire. (00:57:55)
Revealing mistake: When Evelyn is hanging the clothes after washing them, they are already dry.
Revealing mistake: When Scott dislocates his thumb to get out of his hand cuffs, they are fully tight. But while he slips his hand out you can see the cuff is all the way loose to allow Van Damme to get his hand out.
Revealing mistake: The visiting nurse was using a non-functioning sphygmomanometer to take Dan's blood pressure. On-screen, the nurse compressed the air inflation bulb about 10 times without the gauge (measuring unit) moving. The nurse compressed the bulb about 10 more times - a ridiculously high number (about 20 total) - but it could not be seen if the gauge ever moved. (02:11:10)
Revealing mistake: When Asher is shooting a bolt-action sniper rifle there's no casing ejecting from the rifle as he reloads it with the bolt. (00:48:30 - 00:49:25)
Revealing mistake: When Kurt and Elisabeth are looking at the painting of the Third Reich caricatures, in the shot focusing on them, a little girl in the background can be seen glancing at the camera. (00:01:45)
Revealing mistake: Davey at the beginning of the movie is looking at the newspaper he's delivering to Mr. Wayne Mackey. Just from a glance at the page you can tell that something is off, since the article supposedly about a missing boy appears to be written entirely in first person. Upon closer inspection, turns out that it's filler text from chapter IV of Robert Louis Stevenson' s "Treasure Island". (00:01:30)
Revealing mistake: While they're finally on the rapids, the girl blindfold keeps changing position from her neck to her forehead. (01:40:59)
Revealing mistake: When Red hits one of the demon bikers with his vehicle after he shoots it with an arrow, as the vehicle flips from the impact that there is actually nothing there he hit. (01:16:20)
Revealing mistake: Eve says they need to make sure nobody gets shot, so she picks up Franklin's pistol and takes out the magazine to store them separately. However in this shot the magazine is completely empty with no bullets anyway. (00:53:40)
Revealing mistake: When the agent is questioning Fat Freddy after the cop finds him with coke and a gun, she puts a phone up to his face and says "say cheese." She holds the phone up to his face with the screen facing him. You hear the click and beep of the phone taking a picture, but when she turns the phone around, it's still on the locked screen with just the background and a clock. (01:06:45)
Revealing mistake: Normally I wouldn't consider a bad CGI effect to be a mistake, but when Elise finds the hidden keyhole in the wall in the basement, the effect is comical if you pay attention. The way it appears as she scratches is pretty unnatural, and the pieces of paint that fall practically look like cartoon pieces if you pay attention. The shadow of her left hand also looks a little too sharp compared to the rest of her (somewhat softer) shadow, revealing it was likely rotoscopped in some way.
Revealing mistake: When Bearman and the President are running from the Russians, we see some Russian 4x4's doing a hard turn to chase them. In this shot you can see skid marks from previous takes. (01:15:30)
Revealing mistake: Gone past Waikiki who tells him he knows about the cop, Everest wheels her to the secret door. Batista to open it touches the leftmost corner of the slat. In previous close-ups, the button was at much greater distance from the wall, surely not just an inch. He's pushing no button, just pretends to. (00:56:30)