Corrected entry: When Aang is talking to Koh, Koh says that the Avatar tried to kill him in a past life, 800 or 900 years ago. Later on in the show, when Aang is on the Lion Turtle, it is revealed that it was Avatar Kuruk who tried to kill Koh. Kuruk was the Avatar before Kyoshi, who was born 400 years ago, as was revealed in The Warriors of Kyoshi. There is a 400 year gap between those events that doesn't fit together. If Kuruk was 400 years old, it would contradict what is stated in Avatar Day, because there, they said that Kyoshi was the oldest Avatar, at 230 years old.
Corrected entry: When Aang goes into The Avatar State because he found Gyatso, statues and paintings of the previous avatars begin to glow all around the world, including the Fire Sage's temple. They act as is this was the first time, but Aang already went into The Avatar State before this point, when he thrown off Zuko's ship in the previous episode.
Corrected entry: Roku dies at the end of the episode because he is about to be engulfed by a pyroclastic cloud. It is made clear that when the Avatar is in imminent danger, The Avatar State is triggered. So it should have triggered, saving Roku, but that couldn't happen for obvious plot purposes, even though it defies what they said earlier.