Kugelblitz - S3-E4
Revealing mistake: At the beginning of the episode, as Sissy is signing the papers under the pseudonym Dana Pocket, she is holding cash in her left hand. The words "pictures" "and "film" can be appreciated on the faces of the bills, revealing this is fake money, often used in Hollywood productions.
Revealing mistake: The ghosts often cast shadows.
Suggested correction: You can also hear their footsteps. But I'm not sure this is a mistake, just their own perception. Within the ghostly world they appear and act just like they would in life.
The ghosts are manifestations of energy, therefore they have no physical body to block light. Even if in the ghostly world, physics are physics and there should be no shadows.
When in Rome - S1-E3
Revealing mistake: Will and Frankie are in a boat. In the first wide shot the boat is going rather slowly, in the next shot they are speeding many times faster, and the shot is erratic, showing that the action was speeded up. (00:02:05)