When Manjhi is taking bus to his village, we can see instructions on bus door in Marathi. Marathi is not the language of Bihar.
In Ganga Aarti scene, we can see Rupa undergarment vinyl hoarding in background. The logo of the brand is very recent and not from the period depicted in that scene.
The bus Manjhi Boards has a Yellow colored registration plate with Black font on it, which came much later in India. At those times the Number plates were White board and Black font for commercial vehicle.
In the Hospital scene where Phaguniya is gravely injured and is taken to a hospital. There is patient being taken on stretcher with a plastic bottle of glucose. Plastic bottles came into usage much later. This should have been ideally a glass bottle.
When Manjhi is taking train for Delhi, on arrival of train, we can see thin plastic bags flying around. Thin plastic bags were introduced in India much later than the period depicted in that scene.
When Manjhi is thrown out of the train by the ticket checker, we can clearly see his right leg's big toe. But as seen previously in the movie, he had already cut it off due to the snake bite.