Audio problem: When Winston says "Bugger." at the start of the film when he has the cigarette in his mouth, his lips are most definitely not in sync with the word. And it even sounds dubbed over.
Continuity mistake: In the torture scene near the end of the movie Winston is lying on the rack. One of O'Brien's aides removes the shackles of Winston's right arm, but leaves the one on the left arm fixed. Next shot: O'Brien tells Winston to get up, and he does, although the shackle on the left arm has not been removed. Minor mistake but noticeable.