Rule 48.8 states you cannot overtake under the safety car. Mercedes argue Verstappen did this. The normal punishment would mean a 5 second penalty, meaning Hamilton wins.
Rule 48.12 states that when the race director allows lapped cars to overtake the safety car, the safety car must stay out until at least the end of the following lap. This did not happen, it went in on lap 57 rather than 58. This meant there was a last lap shootout between Hamilton and Verstappen, which Verstappen won. Mercedes argue that this was a breach of the rules. Unlike the above, no driver did anything wrong, so the remedy is unclear although
@blueinsa believes this would hand the race win to Hamilton