Thorpe Park - S1-E3
Factual error: The same number plate can be seen on two different vehicles in this episode. The registration M483LTH can be seen on the hearse and then on Simon's car when parking. No two vehicles in the UK will ever share a number plate. (00:11:10 - 00:12:30)
Land of Hold/Penny Henny - S2-E17
Deliberate mistake: When Garfield brings Jon to the broken TV, the scene's animation is still unrendered. (00:01:04)