Factual error: 3 plutonium balls would weigh 180 kg, each one 60kg, they wouldn't be able to single hand it, not to mention throw a suitcase with 3 of them inside. Critical mass is 11kg for ball shape so they wouldn't be even able to make those balls.
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)Sammo
Other mistake: When Benji takes off the Wolf Blitzer mask, he continues to talk with the anchorman's voice until he takes off the voice altering tape too, but when Walker realises that he is not talking to Solomon Lane and proceeds to rip off the mask, Benji talks with his own voice without taking off the tape.
Continuity mistake: When Benji is sitting back to back with Soloman Lane to duplicate Lane's face, his jacket is green, then they cut to face Luther asking whether Benji is OK, when they cut back, Benji's jacket is the same brownish color of Lane's jacket. Later, Benji wears the green hued jacket again when talking to Luther and Elsa. (01:23:30)
Plot hole: On the plane they are told they have 2 mins to suit up, then once suited up they have a further 10 seconds before the rear door opens. 2 minutes is not enough time to put the equipment on to do the halo jump.
Factual error: When Ethan enters Ramstein Airbase, he drives a BMW with a German license plate that can't possibly exist. The only German license plates starting with digits are for official diplomats. There is none starting with 881, the highest is 205 anyway. Another mistake is that even if it was a car of a diplomat, the license plate would have additional lettering next to the country letter D (for Deutschland), in Germany that would be CC or CD.
Deliberate mistake: When Walker leaves the tunnels in London and Hunt follows him, they both start their way to the Tate Modern Museum at Queens Head Passage / Paternoster Row. While Hunt is being chased and cannot choose his route, besides not knowing about Walker's destination, Walker deliberately takes a detour to Blackfriars Station and the bridge, even though he could just have walked a direct line from St. Paul's Cathedral towards Tate Modern using Millennium Bridge to directly cross to the museum and his getaway. The whole chase sequence would be obsolete. (01:31:58 - 01:36:56)
Continuity mistake: During the rescue of the White Widow, she stains her clothes with blood, from the left bust to the side, in the next scene, the stain is no longer on her bust, only on the abdomen and very small. (00:40:05 - 00:40:28)
Continuity mistake: The fight scene in the nightclub toilet between Hunt, Walker and who we believe is Lark is brutal. Both Hunt and Walker take several blows to the head and face, but when it is over there isn't a mark on either of them.
Continuity mistake: At the start of the truck chase the road is completely dry and it's sunny, as they go over the bridge the road is completely wet and it's overcast, then the road is dry and it's sunny again.
Continuity mistake: When the truck gets knocked into the river it is almost submerged by the time Ethan reverses the truck. Cut to part of the truck chase and then back to the river - the truck is sinking again and the driver and passenger are getting out. The truck is also at a different angle to when it first went in.
Continuity mistake: During the BMW/Bike chase in Paris, Ethan crashes through some parked motorbikes and drives away, the rear window on the passenger side is completely open. Before and after this scene the window is shut.
Continuity mistake: The little projector in the Odyssey book only lights off at the end of the briefing video, but in the following frame when Ethan closes the book it's already back inside it. (00:04:50)
Continuity mistake: When Hunt reverses the truck into the street and drives off, dumping the bad guys onto the road, the doors are swinging about as they should be, but for the rest of the chase they are shut and latched so they can't come open again. This has to be done manually.