Plot hole: When Fluffy saves Chloe she calls out 'thank you Fluffy'. Cruella never told her the dog's name so how did she know it?
Factual error: The train leaves for France from St Pancras station (clearly identified by The Shire pub), which is Northbound and has no connection to go back south for France.
Continuity mistake: When Cruella (Glenn Close) gets turned into a cake, the dogs squirt coloured icing all over her face. A few seconds later she falls against a glass door with her face, and red icing is smeared all over her right cheek as she slides down the glass. In the next cut the arresting officers are taking her into custody, and she has a neat yellow blob of icing on the same cheek, and all the smeared red icing is gone.
Continuity mistake: When Cruella has her photo taken on the magazine, she has black hair on her right and in another, the black hair is on the left.
Continuity mistake: The train that leaves the station is the Flying Scotsman but soon afterwards the train is shown and the engine is a different one.
Continuity mistake: When Oddball's sweater is unravelling and she ties up the bad guy's feet, the next scene shows her at the window and the sweater is fine and has no hanging thread. The very next scene the thread is back.
Continuity mistake: In all the shots of Oddball before, even the computer generated Oddball, her eyes were brown. However, after Cruella gets baked into a cake, when Oddball looks down at her eyes are blue. They switch to a different shot, then come back to her and they're still blue. Later they're brown again. (01:31:02)
Continuity mistake: Cruella throws Oddball into the batter, but a few minutes later, after Cruella has been baked, they call for Oddball, and she is completely clean.
Factual error: In the scene where the train is leaving the station, a locomotive warning bell is heard. British trains do not have bells.