Audio problem: At the beginning of the episode when Cordelia leaves with Pierce, she says, "Don't mind him". But her lips don't match the words.
Sleep Tight - S3-E16
Audio problem: At the end of the episode when Holtz jumps into the dimensional rift with Connor, we hear Angel yell "no" twice. But his lips don't move on either occasion.
Benediction - S3-E21
Audio problem: When Cordelia has her vision about the vampires at the bar, her lips don't match the words "Vampires, a gang of them".
Audio problem: During Lilah's failed attempt to rescue Angelus, when Gunn shoots at Angelus with the tranquilizer gun, Angelus passes out then hits the ground. When he is about to pass out, we hear the sound effect of him hitting the ground before he even begins to fall over, and instantly in the next camera angle he hits the ground. (00:08:20)
Audio problem: When Gwen says to Garret, "I know the risk, but I'm going in there with or without your help," her lips keep moving as if she's still speaking.
Audio problem: The lips of the Newscaster's who reports on Conner taking over the sports store do not match what she is saying at all.
Answer: Everybody including Angel saw her. After helping them and then being left alone to talk to Angel, Cordelia says that the Powers That Be let her come back one more time to help them. After Angel gets a call saying that she died, he realises that it was her spirit that was helping them the entire time.