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.
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.
Answer: Breakdown trains help the engines back on track.