Due to a Director’s decision, the geography of Hogwarts was changed, causing Hagrid’s hut to be by a massive hill and steps, instead of being a little way down from an entrance to the school. From the time between the second film and the third film, the hut also underwent a change in it’s size and design too. In the Philosophers Stone and Chamber Of Secrets, the hut consists of only one room, but from the third film onwards, it changes.
The Director’s decision on the change of the layout of the grounds also differed the location of the Whomping Willow, which can be seen in Chamber Of Secrets when Harry and Ron crash land the flying car, which is quite near the grounds, and yet then in Prisoner Of Azkaban, it is not seen anywhere near the grounds, but near some very rocky looking land.
Lots of times in the HP films, can there be seen a crew members arm or other minor movement which shouldn’t be there, but one of the biggest mistakes that they made when filming the scene in Chamber Of Secrets where Harry is put up against Draco, is that on the far left of one of the shots looking towards Malfoy’s side, you can blatantly see a cameraman knelt down in amongst the children.