Thomas and the Billboard - S12-E1
Revealing mistake: At the beginning of the episode, Henry has Gordon's face.
Thomas and the Billboard - S12-E1
Other mistake: In the opening scene when Edward and Henry can be seen going into Knapford, Henry is wearing Gordon's face mask.
Thomas and the Billboard - S12-E1
Visible crew/equipment: When Percy leaves the station, a camera shadow is visible.
Thomas and the Billboard - S12-E1
Visible crew/equipment: At the very start of the episode, a stage light is reflected off Gordon's coaches.
Answer: Breakdown trains help the engines back on track.