Haven't seen it yet since it's not out yet in the U.S., but a couple of possibilities come to mind:
1. As PC pointed out in his post, if it is just a situation where a James stops singing and the note continues, it could be reverb/delay exending the note a bit after he stops singing it. That is fairly common. I don't know if they using a backing tracks for James' vocals, but it could also be the delay from a backing track, as well.
2. Could be an audio/video sincing issue where the footage for that brief shot is either a second or two head of the audio or is footage from a different part of the show that was inserted there by mistake.
Hard to say more without having seen it to know what you are referring to.