When Max tries to run away & gets pulled back along the floor by Vecna, her hair changes from pony tail with scrunchy to without.
Dr. Owens takes Eleven to an abandoned ICBM silo in Nevada. Nevada is not a state that has (or had) ICBM silos.
Murray and Joyce drink roughly the same amount of drugged coffee at the same time, and Murray is unconscious first. Joyce would be unconscious first, since she has less body mass.
When escaping the Kamchatkan prison on a snowmobile, Hopper is shown with bare head, hands and feet. With temperatures far below freezing point and wind, body heat loss would be tremendous and death by hypothermia would occur quickly, or at least extremely severe frostbites leading to necrosis of various body parts.
At 0:44:53 -the peanut butter in the jar that Hopper has just opened has already been disturbed.