Continuity: At the start, in shots from the stage towards the audience, all of the fires are lit, but in a closer shot of the audience near the front of the stage, at least one of the fires is out.
Continuity: When Inspector Uhl is inspecting the theater prior to the arrival on the prince, he is speaking with Eisenheim. When Uhl says "I have been puzzling over how it works", Eisenheim is standing with his arms behind his back. When it cuts his arms are crossed.
Visible crew/equipment: Near the end of the film, Chief Inspector Uhl is in Prince Leopold's office. In the close-up scene when the two argue, you can view the boom mike, going from one character to the other, in the reflection on the brass table lamp.