Other mistake: The narrator says that Thomas' driver puts syrup in the lion, but actually, Thomas fireman puts the syrup on the lion. This is identified by his moustache.
Character mistake: The narrator says that Thomas had never delivered the mail before, but he did in Season 4.
Other mistake: Mavis and Cranky should've realised that Thomas woke them up the first time he blew his whistle.
Continuity mistake: Thomas says that Mavis and Cranky never make mistakes, but they have in "Mavis" and "No Sleep for Cranky."
The Biggest Present of All - S13-E16
Audio problem: When Henry and James are at the quarry, their whistle sounds are played out of order.
Answer: Butch the breakdown truck must have pulled Gordon's tender all the way up the rails so the breakdown train can reach it and also Butch helped to get Gordon close to the winch.