Revealing mistake: Very obvious copy and pasted dogs (even standing in the same position) whenever there's a general view of a crowd in the main hall.
Chapter 7: The Reckoning - S1-E7
Revealing mistake: There's some sleight of hand involved when Cara gets her cup of tea from the repurposed IG-11. Maybe it was costly to have the animatronic arm working to the point of actually supporting the cup and hand it to her, so pay attention to what Cara actually does; Gina Carano is ALREADY holding the cup, taps the mechanical hand with it as if the fingers just released it from their grasp, and retrieves it. (00:11:50)
Kugelblitz - S3-E4
Revealing mistake: At the beginning of the episode, as Sissy is signing the papers under the pseudonym Dana Pocket, she is holding cash in her left hand. The words "pictures" "and "film" can be appreciated on the faces of the bills, revealing this is fake money, often used in Hollywood productions.
Revealing mistake: When the protagonist and Uncle Six battle on top of the escalator, Six gets thrown off, landing downstairs. Very much like a pro wrestling Irish whip, it's quite noticeable how the victim is running towards the move before he gets pulled, with a cut to try to hide the lack of any push from the other hand or forceful twist. (00:12:15)
Revealing mistake: The Wonderland gang henchmen dispose of the Crows' van through fire that causes a nice, clean, completely fake CGI explosion, looking entirely disjointed from the rest of the background. (00:02:00)
Revealing mistake: Angelica and the other children are about to crash through the door to attack Lyra and Will. As Lyra runs past a cabinet, a lamp sitting on top is knocked over and crashes to the floor. Dafne Keene, who plays Lyra, reached over and very obviously pushed the lamp to the floor.
Revealing mistake: Multiple times when we see the speedometer of the minivan, the RPMs aren't moving. The car's shifter is also noticeably in park. This is obvious as its higher, whereas if were in drive, it would be lower. Even during the most intense moments, the RPMs never change. The car is obviously being towed by a camera vehicle.
Revealing mistake: The ghosts often cast shadows.
Suggested correction: You can also hear their footsteps. But I'm not sure this is a mistake, just their own perception. Within the ghostly world they appear and act just like they would in life.
The ghosts are manifestations of energy, therefore they have no physical body to block light. Even if in the ghostly world, physics are physics and there should be no shadows.
Revealing mistake: The main character gets into a short wrestling match on the landing of a star well. The bad guy fires a shot over the main character's shoulder, which should have hit the wall he was leaning against, but no damage is shown on the wall. (00:05:40)
When in Rome - S1-E3
Revealing mistake: Will and Frankie are in a boat. In the first wide shot the boat is going rather slowly, in the next shot they are speeding many times faster, and the shot is erratic, showing that the action was speeded up. (00:02:05)
Revealing mistake: When Dyatlov goes outside the control room to check on the situation after the explosion, his collar and button strip on both his shirt and coat change positions. When he's in the room, it's facing his right, but when he leaves the room and see graphite on the ground below him, it's facing his left.
Chapter Four: Housechilling Party - S1-E4
Revealing mistake: When Ryan's iPhone vibrates with a text message from his mom, the text message is timed 5 hours before the time on the lock screen. An immediate message would normally indicate the time received as "now." (00:06:45)
Revealing mistake: When The Wraith is parked at the convenience store, wet tire prints are seen on the concrete from previous takes of the car backing up and turning off the store's lot. This is confirmed later as Charlie Manx actually reverses the car when he drives off the lot.