Aha! The OP and the film present not the same problem (didn't watch the film until now).
In the OP the expression is given as 9-3/1/3 +1, which also the film says will be 9. But the graphical presentation of the expression really translates to - as the film also says, 9-3/(1/3)+1 which gives 1.
So, if you solve the expression as presented in the film you get 1. I assume that is the original problem. And if you solve the (incorrect) version of the formula in the OP, you get 9.
BTW: I'm a bit surprised that this (the formula given in the film) has gone viral as a really difficult problem, and that only 60% could solve it, as this is ground school mathematics. Hmmm.. sounds a bit arrogant. Does it?
pibbur who prefers formulas like e^(PI*i)+1 which unambiguously is 0.
PS: I've decided to, when I become the most powerful man in the world, to force everyone to write formulas using RPN (postfix notation). DS.
PPS: And also to exclusively use binary : 1001 1 11 1 11 / / - + DS.