The chandelier is gold coloured but the shots of the wreckage shows it a gray and in the two shots of it there's no sign of bodies.
When the Phantom starts to saw through a link holding up the chandelier it can be seen that it's already cut through.There's then a mixture of shots of him sawing from one side then the other, one where he seems to have started and at the end one showing no cut.
When Anatole is pursuing the Phantom over the catwalk, the ladder wobbles in long shots but is very stable when the actors are in close-up.
The name of the opera being performed in the opening scene is given as "Marta" on the printed sheet music but "Martha" on the back of the "flat" (the backdrop used at the back of the stage).
There appears to be an error in the credits. Nelson Eddy is attributed as a "sculptor: bronze statue of Christine DuBois." The bust statue was white; hence likely plaster was meant to appear as marble.
When Christine takes the mask off from Phantom's face, we see that his scar reaches the low area of his right cheek, even the right eyelid is slightly fallen. But before that during the entire film, we never see a single mark of the scar on the uncovered area of the Phantom's face, not even the fallen eyelid through the mask.
When the phantom strangles the police man, the officer has a cape on. When the inspector finds the body, the cape is gone but the rope is around his neck.
(at around 40mins) There is an prominent cymbal crash in the orchestral score which happens at about a second before the actor actually clashes his pair of cymbals.
When Claudin (Claude Rains) is being tested by the maestro, his fingering of the violin's strings do not match the vibrato produced.
Erique Claudin's concerto is for piano and orchestra, even though the instrument he plays professionally is violin, not piano.
The diva Lorenzi comes to the front of the stage to start her aria and starts screaming before the chandelier starts to fall.