When Fantine is sick and in bed, she coughs up blood and smears it on her face. In the next scene, no trace of blood is on her face.
When Inspector Javert is at the home of Cosette and Jean ValJean, he writes a letter and asks Cosette for an envelope which she produces for him. The type of pre folded, flap envelope that Cosette gives him would not have been invented or for commercial use in 1832, the time period of Les Miserables.
Rather, correspondence would have been folded inside another sheet of paper and sealed with a wax seal and brass sealing ring or tied with a string or ribbon.
After Cosette is told by Valjean about his past and they leave the house. Marius goes to the house and starts banging on the door shouting for her. The door is equipped with a Yale lock, not invented until 100 years later.
After Javert causes the horse and carriage to flip in the pursuit of Jean Valjean, you can clearly see the large pneumatic device which was used for the stunt under the carriage. As Javert stumbles further along the pathway in pursuit, the carriage is seen in the background and the device is now gone from under the carriage.
During the revolution, several shots show the Saint Vitus Cathedral in Prague.