Well, I found mine. Not to bore you all, but I exported my footage in separate layers, with an Alpha Channel as a PNG sequence. The point of this spiel is that one of my layers (the boy) was one frame out of sync, so he overlaps on every cut. Very noticeable on a projector, which is rather concerning so I've managed to source the rogue file and make a new edit which I should be able to export over the next few days. Hopefully the gaffe is only noticeable to me because I've seen the film so often, but who knows.