When de Winter is showing the honeymoon film, he tells Mrs. de Winter "this is where I set the camera up on the tripod". However, the image they're watching zooms in (this is before the cinematographic image zooms in on the entire film-viewing scene in the movie, itself). Since the camera was on a tripod, it wouldn't have been able to zoom by itself since de Winter was posing with his wife at the time, not adjusting the camera.
When the new Mrs. De Winter first enters the room to do her correspondence, there are three books on the table. An establishing shot shows that the book on the left is labeled "menus", and the one in the center is labeled "addresses". Mrs. de Winter picks up the one on the left, and it is now revealed in a close-up to read "addresses" on the cover.
In the Monte-Carlo Hotel Lounge, the Narrator and Mrs Van Hopper are having coffee. The Narrator's coffee cup, then a newspaper are in her right hand between shots without sufficient time or obvious motion to change them.
When Mrs. Van Hopper begins to put out her cigarette into the cold cream jar, the jar already has a cigarette in it. At the closeup of the jar, the original cigarette is gone. She puts in a cigarette at an odd angle but when the close up is over, we again see only the original one.
Twice during the movie, Maxim leaves Manderley to travel to London, once by train and another by car. On each occasion, he manages to get back before dark. Manderley is in Cornwall, as far from London as you can get, and even with 21st century roads, cars and trains, that feat would be impossible. This error is copied from the novel.
When Reginald Denny's character is in the study with Joan Fontaine's character he pulls out a file folder from a file cabinet and it's in the American format for 8.5 x 11 inches rather than the English A4 size. A4 is a bit narrower but longer than the US letter size standard and its paper would not fit the file folder Denny is holding.
In the outside take of Manderley seen in the scene where the Narrator stares at one window being closed, it's a miniature, as is the 'Mrs Danvers' dummy dressed in black. You can realize this by the motion of the window as it's being closed, not in a continuous way, but by little fast jumps, which look too unreal.
At the inquest, when Ben begins to testify, the clock reads 11:48. A few minutes later when Mr. de Winter is recalled, it reads 1:53. But then when Mrs de Winter faints, the clock reads 11:48 once again.