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: Parzival heads back to the Halliday Journals to watch the scene of Halliday and Morrow parting ways again. There is glass between him and the scene and some camera angles show Parzival through the glass from inside with the scene reflected on the glass. However the reflection is wrong. Morrow is standing on the right with Halliday on the left, but when showing their reflection in the glass, their positions are not reversed. (00:23:45)
Revealing mistake: When Max and Annie are driving the car towards the Bulgarian's plane, there are a few exterior shot of the car, and you can blatantly tell that "Annie" is a stunt performer in a bad wig. Her head and especially hair look MASSIVE in these shots, compared to how small her head and hair usually are. (It's especially noticeable in the shot that's following the car from behind).
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)
Revealing mistake: When Scott is fighting Ghost, as Pym is planning to dive, Ghost throws Scott through a wall and you can see the braking cable around his/the stuntman's waist and across the floor. (01:16:48)
Revealing mistake: The anchor rope around Maddy's neck is loose enough for her to remove.
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: When the bartender recognizes Harold and calls the cartel leader, his phone screen stays on instead of turning black and shows that he's still on the lock screen displaying the time, not actually calling anybody. (00:49:30)