Early in the movie we clearly see Mr. Waikiki shot by small arms fire. He later tells the nurse he was shot by a 45mm weapon. What he should have said was that he was shot by a .45 caliber weapon. 45 millimeters is about 1.75 inches and is certainly not small arms fire and does not match the bullet holes we see inflicted upon him.
Waikiki is told to look for a 74 Chevy Nova. However, the Nova he drives off in is a 68-72 model. The body style changed for the 73 model year.
Waikiki pulls back the chamber of the white gun in the 64th minute. Problem is, it's a revolver and shouldn't have a chamber.
After Honolulu died when his life support was cut off there is the standoff when Waikiki gets a hold of Acapulco. He shoves his head into a 3D printer and turns it on to kill him. Except the whole reason Honolulu died was the power to the entire building was cut off, so the printer would not have been operational.
Both Waikiki and Acapulco were able to create guns inside the weapons-free facility using parts made on a 3D printer. However they would not have been able to get the bullets to use the guns, though they are shown to fire them later.
The Nurse's obvious flat lenses on her reading glasses.
In the early shootout scene, the robbers in the lane are spotted by several police who are repelling a protest outside the lane. It seems unlikely that no other police noticed the three officers shot down, and no one came to help them.
When Lev threatens the first hostage during the heist, his lip movements don't match the words.
About 30 minutes, The Nurse goes through the "secret hallway". As she makes a left turn, there is a (lighted) green exit sign (where a hallway supposedly ends) which she passes. The camera shows it from the side. However, the front can be seen briefly as the camera angle changes.
The scene where Everest puts on his tag and pulls down the switch to light up the "Hotel Artemis" sign board, the hand is too skinny to be Dave Bautista's hand. It clearly is someone else.
When Nice is counting down in French to when her bomb explodes, she misses out dix-huit (eighteen).. This may be deliberate because, at times, she seems to struggle to keep up with the countdown.
During surgery, the Nurse refer to a "bicep." A trained medical professional would know that the correct word is "biceps"--singular as well as plural.
Everest is strict on following the rules and yet allows Mo to speak directly to the Nurse on the Talkie, risking for everyone around her to hear the conversation.
Nice goes through the effort of getting the piece of porcelain embedded in the wooden chair despite the fact the previous hit necessarily blunted the edges.