In the character montage at the beginning of the movie, Mike the Mouse is given a penny by a baboon. Mike reaches out and grabs the lapels on the yellow shirt, the next shot he is pulling the green sweater.
When Big Daddy, Stan, and Barry complete their heist, they emerge from a manhole. When they hear police sirens and the camera changes the angle, the manhole has disappeared.
During the final presentation, some keys of Johnny's piano are replaced by pieces of wood. However, when he starts playing, all keys are pearly white.
In the final presentation, a gorilla sitting behind Meena's family changes shirts between shots: first, he's wearing a white shirt with blue sleeves; then, he's wearing a plain green shirt. A third glance shows him wearing, again, a white shirt with blue sleeves.
Ash's boyfriend Lance plays left-handed with a left-handed guitar at the start. There's a scene a short while later where Lance is sitting on a sofa playing his guitar right-handed and the guitar has switched to a right-handed model. Further on in the film, Lance and his guitar are left-handed once more.
When Rosita's automated recording plays on the tape recorder, there's a die sitting on the table. Number "1" is on top, and number "6" is facing the camera. All six sided dice are manufactured with the 1 on the opposite side of the 6, so this representation is inaccurate.
When Mike the Mouse is singing and the helicopter picks him off the ground (which also would not happen), he is singing facing the side of the microphone. This wouldn't happen because a mic only takes in sound from the end of the mic, not the side. This was invented to stop reverberation from other sound sources (especially other instruments) on the stage.
It is physically impossible for Meena to have reached the ledge, as her trunk just isn't long enough.
Ash's guitar has fret inlays on the 4th, 6th, 8th and 13th frets. Normal positions for inlays are on the 3rd, 5th, 7th and 12th frets. The inlays don't affect the playability of the guitar, but they serve as visual guides for key positions on the fret board and can confuse a player who relies on them.
It is physically impossible for Rosita's concoction to have a train toy attached to the ceiling, as it'd fall from the rails.
The last time that Buster Moon rides his moon down to the stage he starts at the top facing the audience. The camera view changes to the audience laughing, then moves to behind the moon to show Buster facing the wrong way, and looking up as if in surprise. He then turns to face the audience and continue his introduction. However, it is possible he just changed positions off screen to jest with and captivate the audience.
When Rosita comes home after the first day of rehearsal and checks on the kids to see how her automatization worked, the alarm clock is back on the table. When it went off in the morning, it fell off of a stack of books and onto the floor. There was no way for it to be put back without someone putting it there, and since no one even noticed she was gone, they wouldn't put it back. It is, however, possible that the concoction had a mechanism that would put it back up.
During his final song number, Mike is pulled up by the draft from the helicopters and struggles to hold on to the mic and its cable. Moments later, when the helicopter leaves the scene, he plummets and swings himself to safety on the microphone, which now seems to be attached to a hanging cable anchored somewhere quite high in the air (which additionally contradicts the appearance of the mic when Mike first comes out, where the cable rests on the feet of the microphone stand).
In fact, if watched carefully, in the shot where the helicopters departing one can see the cable is extending from ground to air and once helicopters leave and upward suction effect vanishes, part of the cable sticks somewhere high and the part Mike is holding hangs down. However, when the song is finished, no cable extending from ground to upper section is shown.
During the entrance scene, when Buster Moon narrates "his plans to become the first koala bear in space were suddenly... toast." Depicts a common mistake that a Koala is a Bear. In all actuality it is a Marsupial. However, this may be intentionally written in the story line because of the widely known use of this misnomer and also because koalas look like small bears.
During the audition, Moon writes with his left hand, but after it's done he writes with his right hand. That could indicate he's ambidextrous, and therefore writes with both hands.
When Rosita digs into the cabinet, the items inside it make glass clinking sounds. When the camera turns, there are no glass objects there.
When the workers build up the theater, the roof chandelier is installed upside down, so that its light beam would be above the ceiling.
When Johnny gets the call from Buster to put on the show anyways, he rides out of the garage on his skateboard, but later as they're working on getting the theater set back up, he somehow has the truck, as he is using it to help lift something heavy.
It seems very strange that the gorillas are wearing leather coats, considering that leather is made from animal skin, and everybody in the city is an animal.