During a majority of Little's timeline (which is supposed to be set around the 1980s or 1990s), modern day cars are shown driving around - especially when Juan drives Little around in his car.
At around 1h 04m 30s, when Chiron is entering the school and opens the second door pushing the emergency handle, the scene is instantly cut to show the room from the inside to see him enter, but, when he does enter, the door can clearly be seen being pulled, not pushed.
When Chiron dreams about Kevin after their phone call, they have not seen each other since high school and yet Kevin is portrayed as an adult. Chiron would not know what adult Kevin looks like.
Just before Kevin and Little wrestle in the grass, Kevin's gold chain goes from under his shirt, to over, to under again.
When Juan drops off Little at his home, modern CDs are shown in the car.
When young Chiron eats as a guest he is seen holding his fork differently than the adult Chiron in the diner at the end of the movie.