Factual error: The problem with firing a cannon on steam power is to have the boiling water build enough pressure inside the barrel, with no leaks or openings to release it before its time. The professor's scarf and the plug hammered into the fuse hole (which also flies off just before the shot) wouldn't be good enough as pressure restrainers.
Revealing mistake: It is obvious that the night scenes were filmed in broad daylight, since clear shadows are still cast on any available surface.
Other mistake: When Krolock ambushes Sarah in her bathtub, he bites her well above the place where the bite marks later show.
Factual error: I don't know whether they had bubble baths in an isolated village of the late 18th/early 19th century; and even if they did, the foam in Sarah's tub looks remarkably untouched (except for the blood) - considering that she had just been thrashing around in it when Krolock attacked her.
Continuity mistake: The window in the crypt is first seen to the left side of the caskets used by the Count and his son. Later when the Professor and Alfred attempt to enter the crypt through the window, it is directly behind the caskets. In the earlier view, the wall behind the caskets was solid and had the stone image of another grave covering in the crypt wall visible.