Wagner was shown crossing the Alps with his piano, the size of a parlor grand piano. Yet when he is seen in Venice, the gondola was shown hoisting a full-size concert grand piano, not the smaller parlor grand shown earlier.
When Wagner speaks at the political meeting, the vertical German flags in the background have the wrong sequence of black-gold-red, while the ones draping the podium are the correct black-red-gold ones. (The flags are the 1832 Hambach Festival flag - the modern German flag dating from 1848 was developed from the Hambach colours)
When Ludwig is wading into the water to drown himself, automobiles are seen driving on a highway on the far shore.