Apologies if this has already been mentioned. Too many posts to check.
There’s video evidence that two Argentina substitutes were actually on the field of play before Messi scored their third goal. I don’t think anybody outside of France is seriously suggesting they should have disallowed it but:
Official FIFA rules state: "If, after a goal is scored, the referee realises, before play restarts, that there was an extra person on the field of play when the goal was scored the referee must disallow the goal."