Gordon and the Engineer - S11-E6
Continuity mistake: When Gordon is at the signal box, he drops off his coaches on his track and leaves. When he comes back with the mechanic, the coaches are gone.
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.
Character mistake: Throughout the episode, a "Bufferbeam" is referred to as "a buffer." Also, at the beginning, the narrator says that the diesels are shunting coal trucks when they are really shunting flatbeds.
Revealing mistake: In a shot of Gordon arriving at Brendam Docks, only half of his tender is visible.
Continuity mistake: Henry pushes Percy onto the coal tipper twice.
Plot hole: Percy was blamed for being on the coal tipper when it was Arry, Bert, and Henry's fault. None of the three got consequences. Also, why would the workmen tether Percy or even activate the coal tipper when they knew he was an engine?
Audio problem: When Oliver arrives at the station, he has Percy's whistle sound.
Continuity mistake: When Thomas hides behind the trucks, there are only 3. But in the next shot, there is a flatbed with a crate on it in front of the trucks.
Audio problem: At the beginning of the episode, Salty has Diesel's horn sound.
Revealing mistake: When the passengers lift Duncan back onto the rails, his trailing wheels are still derailed.
Audio problem: Thomas has James' whistle sound when he passes Sir Handel at the beginning.
Continuity mistake: When Thomas passes Gordon, Butch's magnet is attached to Thomas. In the next shot of Thomas, it isn't. And in the shot after that, the magnet is attached again.
Audio problem: When Thomas and Butch deliver Rosie's wheel, her whistle sound is at a higher pitch.
Flour Power - S9-E26
Factual error: The narrator says "Suddenly, Thomas felt something touch his tender," but Thomas is a tank engine. "Bunker" is the correct term.
Continuity mistake: When Thomas goes back to Maithwaite, Flynn's railway wheels are not touching the rails, but his tires are.
Continuity mistake: After Thomas stops near the bridge, he does not have a Wonky Whistle.
Audio problem: Stepney's whistle sound changes throughout the entire episode. And in the UK and other versions (excluding US), Gordon, Duck, and Douglas have the same whistle sound.
Bowled Out - S4-E18
Audio problem: When James leaves Crovan's Gate, he has Smudger's whistle sound.
Audio problem: When Den and Dart bully Flynn, their voices are swapped.
Answer: He was in the water.