The first segment of the film set in Transylvania, much like the novel "Dracula", is set as if the time frame is in the 19th century with horse drawn carriages, no electricity, and masted sailing ships. However, when Dracula arrives in England, the time period has noticeably shifted to the (then) modern day of the 1930s.
When Dracula's brides converge on Renfield after he has passed out, Dracula enters and motions them away. As they are walking backwards, one bride steps on another bride's dress causing one bride to "catch" another. It is possible that she may have stepped on her own dress.
Dr. Seward threatens to have Renfield confined in a "strait-jacket". Although this is probably a translation convention for the American audience rather than an unintentional slip, a British doctor would say "strait-waistcoat," which is what he says in Bram Stoker's novel and other filmed enactions of this scene.
In the film the peasant woman crosses herself in the Western way - from left to right. However, as she is Romanian, she would likely be Orthodox and would cross herself in the Eastern way - from right to left with three fingers held together.
When the street doors of the London concert hall open to admit Dracula, the orchestra can be heard playing Franz Schubert's "Unfinished Symphony". But in the next shot, an instant later, they are playing the conclusion of the prelude to Richard Wagner's "Die Meistersinger".
When Dracula and Renfield first enter the castle bedroom, the door is closing by itself, hinged on the right side; after a scene shift the door is seen still closing (when it should have been shut by now), but is now hinged on the opposite side.
At one point Dracula gets out of his Carfax Abbey coffin. In the background can be seen the great hall standing set for London After Midnight. A still exists of Lugosi carrying Chandler down these stairs and the scene is in the Spanish version. However, later his coffin is in the basement.
Joan Standing is wrongly credited as a maid, but she was actually playing the part of Briggs (a nurse). Moon Carroll played the uncredited part as a maid. She's the one who faints when Renfield is laughing very scary.