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