Revealing mistake: When E. Johnson first meets, and grabs Sam, flipping him to the floor and holding him at gunpoint, this is obviously not Melanie Griffin, but a stand in. Their face is completely different, and their eyebrows are much, much thicker and fuller.
Revealing mistake: After Cherry has malfunctioned, in various shots, such as when she inanimately lies in bed with Sam, you can see her breathing and blinking. She is supposed to be an inanimate robot.
When Sam goes into "The Sinker" bar, he goes over and talks to Stacy at the table. When he slips Stacy a photo of the Cherry 2000, between a wideshot and closeup the glasses on the table around Stacy change, as he looks at the photo.