Chapter One: Suzie, Do You Copy? - S3-E1
Continuity mistake: In Bruce's hamburger the salad is on the bottom and the bacon is on the top, in the next shot the salad is on the top and the bacon has disappeared, replaced with ketchup. (00:23:05 - 00:27:10)
Chapter One: Suzie, Do You Copy? - S3-E1
Continuity mistake: Steve is talking to Robin about striking out. Two girls come in and Robin encourages him to talk to them. In the first angle his shirt is lower and you can see his chest hair. Cut to the other side as he flips around to talk to the girls, and his shirt has moved up. (00:24:15)
Chapter One: Suzie, Do You Copy? - S3-E1
Continuity mistake: When Billy crashes his car, it stops and breaks down. He moves to the bonnet and a clear hissing from a damaged is audible. Then all the mess happens and the episode ends with the usual cliffhanger. When the second episode starts, Billy's car battery is still up, even with the headlight turned on, and the car starts at once with no problem whatsoever.
Answer: The body was fake, made by the scientists at Hawkins Lab in an attempt to cover up his disappearance and the existence of the Upside Down.