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.
Rosie's Funfair Special - S12-E3
Audio problem: In the US version, Stepney says "Oh my!", but he doesn't sound shocked and his mouth doesn't match the words. In both US and UK versions: he blows his whistle multiple times, but it only emits steam once, and it sounds like Thomas' at a slightly higher pitch.
Other mistake: Henry was supposed to take Emily's trucks to the Coaling Plant, but he takes them to Knapford Yards instead. The narrator also refers to Knapford Yards as the Coaling Plant.
Continuity mistake: When Salty gets blocked by the trucks, his face increases in size.
Saved You! - S12-E10
Continuity mistake: After he is rescued by Thomas, Toby's face changes size between shots.
Gordon Takes a Shortcut - S12-E15
Audio problem: Stanley has a different whistle sound. His original whistle sound is essentially Thomas' at a lower pitch, but in this episode, it is Thomas' at a higher pitch.
Thomas Puts the Brakes On - S12-E17
Continuity mistake: Thomas has a brake van when he arrives at the bridge. When Stanley, Thomas, Murdoch, and Rocky start looking for the bricks, the brake van disappears.
Thomas Puts the Brakes On - S12-E17
Revealing mistake: When Stanley shunts Thomas into the yard, Thomas is eyeless.
Thomas Puts the Brakes On - S12-E17
Revealing mistake: In the very last shot of the episode, Thomas and Stanley are faceless.
Answer: He was in the water.