Continuity mistake: On the spaceship, Peter is talking to Tony, and has his hair swept back with gel or similar. When he says "You can't be a friendly neighbourhood Spider-Man if there's no neighbourhood", we cut to Tony then back, and Peter now has a fringe with no gel. In later shots it's back how it was before.
Continuity mistake: When Doctor Strange attempts to use the Time Stone on Ebony Maw, Maw ties up Strange telepathically and strangles him unconscious. Beside Strange is a police car and a motorbike tipped on its side. Maw then lifts the ground he is lying on, but the police car has been replaced by an SUV and the motorbike has disappeared. The shadows also change. (00:23:25)
Continuity mistake: When Thanos brings Vision back to life using the Time Stone, Thanos is standing a couple steps away from him after bringing him back. Wanda then tries to stop him, and it cuts to a wide shot where he suddenly is a couple of steps closer with his hand suddenly around Vision's neck. Thanos then pushes her with his other hand and in the next shot, Thanos is then reaching to put his hand around Vision's neck even though he was just shown with his hand around Vision's neck already. (02:09:35)
Continuity mistake: When Tony is talking with Pepper, she unties Tony's sleeves from around his shoulders when she points out the unit on his chest. The sleeves are hanging over Tony's shoulders in the wideshot as he says, "I'm just trying to protect us," but when it cuts to the closeup the sleeves have vanished, between shots. (00:12:20)
Factual error: Peter sneaks off the bus using the emergency exit window, which would have triggered an alarm when he released the red safety latch, ruining his stealthy escape.
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)
Continuity mistake: When Peter sees the ship whilst he is on the school bus, he taps Ned on the shoulder and asks him to make a distraction. When he taps Ned on the shoulder, Ned has earphones in both ears, and one of the earphones falls out when Peter taps him, whilst the other earphone remains in his ear. But in the next shot, neither of his ears has an earphone in them. (00:18:25)
Continuity mistake: When Heimdall is stabbed the sword gets into his chest around his heart, in the next scene they take the sword away from closer to his stomach.
Continuity mistake: On Titan, when Tony begins speaking with Spider-Man, Star-Lord, Drax and Mantis, in the shot where he says "We gotta coalesce", Spider-Man is standing a few feet away from Tony and is facing him, but in the next shot, Spider-Man is suddenly standing closer to Tony and is now facing the others. (01:22:50)
Continuity mistake: When Loki reveals the Tesseract to Thanos, the first shot shows him holding it against his fingertips raised above his palm, but when Thor tells Loki he really is the worst brother, the Tesseract is now being held in his palm. Also, when Thanos tells Loki his optimism is misplaced, the Tesseract is still being held in his palm, but when the shot cuts, it is now being held against his finger tips raised slightly above his palm. (00:03:45)
Continuity mistake: Thor says "You talk too much" whilst Thanos has his hand grabbing Thor's head. Thanos' fingers are close together on one side, with his thumb holding the other side. Two shots after, when Thanos asks Loki for the Tesseract, Thanos' fingers are spread apart. Two shots after that, when Thanos says "Or your brother's head", his fingers are suddenly close together again. (00:02:55)