The pan magazine of Milhões' Lewis gun sometimes rotates while he isn't firing. And in some scenes, he is firing, but the magazine doesn't rotate. Most likely the magazine is turned by a motor, which the crew forgot to turn off/on.
On a real Lewis gun, the pan magazine does only rotate after a shot is fired in order to feed another round into the chamber.
Though the film states that the village where Milhais is from changed its name in 1943, in fact Valongo changed its name to Valongo de Milhais long before, in 1924.