The problem is that standard the model believes that the rotational momentum of elementary particles is a conserved quantity. This is correct for the magnitude only but not for the spin direction.
For photons - are not elementary particles - rather than elementary structures of energy, we can fix one of the two major axes but the other two still vary freely.
So the Stern-Gerlach experiment is based on incomplete knowledge and just tells that the particle inertial momentum really changes randomly.
Please do not believe that you can polarize photons 2 x 45o or 1 x 90o and get the same result. The problem is that you neglect the second major inertial axes that shows up in the Goos-Hänchen Experiment...(once twice..)
If you are interested in real physics then study it carefully as most physicist prefer amnesia once they did read it...