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: 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: 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: Just after Proxima Midnight and Corvus Glaive land in the train station, there is a wide shot where they begin approaching Wanda and Vision. In the wide shot, their shadows do not appear to match up with each other, despite being under the same lighting. Proxima Midnight's shadow is positioned in front of her and is quite heavy, but Corvus Glaive's shadow is positioned more to his left and is much lighter than Proxima's. (00:40:20)
Revealing mistake: Right before the scene where Freddie meets with the band to try and make amends, he's arguing with that one man in the rain. After he walks away and it's raining only on him and on the pavement. If you look to the right there is no rain coming down on the grass or trees or anything else.
Revealing mistake: When Chewy puts his hand on Han's shoulder at the end, Joonas Suotamo's finger is visible through the fur.
Revealing mistake: During the big shootout on the freeway at the end of the movie, there is a camera pan over all the cars stopped in traffic. There are no people in any of the cars. The shot is so high that you would still be able to see people crouched down if that was the case. (01:56:47)
Revealing mistake: When Brother Swan goes to blow on the "horn" (which is actually an ocarina), he toots out a few different notes. However his fingers stay completely stationary on the instrument and not moving around on the holes to change the notes. So it would have been just one sound but it plays like 3. (00:29:25)
Revealing mistake: When Tom is fired from Harrods, he is escorted out of the building. Look closely in the glass to the sides of the doors, mainly the screen right, to see a group of people just stood watching the film crew. There is a slight hint of a barrier visible around waist height but to spot the barrier you have to look extremely closely. (00:17:00)
Revealing mistake: As Will and Ben are wrestling for the gun, it goes off, shooting Ben in the chest. When you hear the shot you can see the gun is lying on Ben's chest with him holding it, and it's pointed pretty much at an exact 90° to his side. It would have barely grazed him at best and would have left a long scratch/cut at that angle. Yet as they get up the shot is perfectly centered on his chest and round as if it was a direct shot. (00:24:55)
Revealing mistake: Once Steve gets out of the police car and start shooting at the first merc, the merc hides behind a payphone. Many of Steve's shots can be seen sparking off the payphone that the merc is using to take cover behind, however not one single bullet hole or dent ever appears. (00:46:00)