70 minutes in, as Wolfe leans against the fountain while talking to Mahler, he folds his arms, then in the next shot they're open and he folds them again.
At just under 60 minutes in, Mahler is depicted as being inside a casket, looking at a woman who is dancing on top of the box. The view from inside his casket is though a large, rectangular pane; however from outside the casket the clear pane is trapezoidal in shape and far smaller, just large enough to frame Mahler's face.
When Mahler's train leaves St. Pölten, a sign is visible identifying the town as "Saint Pölten". Yet, the German long script for the town is "Sankt Pölten".
When Bernhard Mahler's wine and spirit brewery is shown it says "EST 1866", referring to the year of founding. However the brewery was owned by then before the marriage of Gustav Mahler's parents in 1860. The year should have either been 1827, the year when it was found by Simon Mahler and his father in law Abraham Bondy, or 1835, when Mahler's grandfather Simon was the only owner.
Gustav Mahler's brother Otto did not commit suicide on the day of Gustav's conversion to Catholicism in 1897; he had killed himself two years earlier, on February 6, 1895.
When near the lake Nick is playing "Frere Jacques" in major key. At the time the scene was set it was common in Austria to play the song in minor key.
In the scene of Mahler's youth the Austrian War Navy, as shown by the Navy flag, is celebrating their "Zapfenstreich" (last post) the tune "Unter dem Siegesbanner" (Under The Banner of Victory) by Franz von Blon can be heard. It was composed in 1895, almost 25 years after the scene's setting.
In his funeral dream, when Stephens (as Mahler) opens his mouth to scream in his coffin, modern fillings are visible in his upper right molars.