Raoul and the Phantom duel in the graveyard over Christine, replacing a scene in the stage show where the Phantom antagonizes Christine and Raoul. Canon Discontinuity: It would be impossible to make a film adaptation of Love Never Dies without breaking continuity with the movie, since it had established that Christine dies in 1918, with the implication that it was because of the flu pandemic.
(And, of course, has never been destroyed by a fire.) The real Palais Garnier, which the Opéra Populaire is based on, also hadn't been completed yet.