The period of time when Jane travels to London in the hopes of seeing Mr. Bingley and Lizzie visits Charlotte at Hunsford is in the winter. The novel mentions that is March, and the trees are just beginning to sprout greenery again at the end of Lizzie's visit. However, in this adaptation, there are lush green fields and foliage at Hunsford throughout the visit.
Throughout the scene in which Darcy proposes to Lizzy in the Parsonage at Hunsford, the clock on the mantelpiece shows 17 minutes past 6.
When Lizzy is outside the Collinses' house, they pan back to Charlotte at one point and you can faintly hear what sounds like a phone ringing, but it is actually a bird song; there are many such instances in the film.
When Lizzy is playing the pianoforte at Rosings, the camera pans across the top of the piano, revealing that no hammers are striking the strings as she plays.
Just outside Longbourn, as Mrs. Bennet is walking her newly-arrived brother and his wife into the house, what she is saying does not match the movement of her mouth and is clearly dubbed.
Lady Catherine notes that the Bennet estate is "entailed on Mr. Collins", "away from the female line", thus signifying that she knows Mr. Bennet cannot have had any sons (because his son would have inherited Longbourne), then a moment later asks Lizzie if she has "any brothers and sisters", rather than, "How many sisters do you have?"