I will conclude here that Mills has all that it needs in GUTCP to produce a quite easy answer to what a deterministic system could be that result in what we see in Aspects experiment and the Stern Gerlash experiment.
Einstein and Ehrenfest was very interested in finding a deterministic model behind the Stern Gehrlach experiment and concluded that the spin up and spin down inside the measurement is not a proper spin up or spin down but that there is a fixed angle at which it precessed. E.g. all other angles was not stable and the system homes in in no time towards those fixed angles. This is also the conclusion of Mills in one of his section in chapter 1 where he discusses this, see the "RESONANT PRECESSION OF THE SPIN-1/2-CURRENT-DENSITY FUNCTION GIVES RISE TO THE BOHR MAGNETON" section. Also, as always with these old fellows and geniuses a more exact QM analysis for this experiment uses this idea and is done in QM paper. So it is not something out of the air. One can most likely test this by measuring the [Larmor frequency]((https://en.wikipedia.org/wiki/Larmor_precession) for a spin up ray after the Stern Gerlash measurement device.
Mills claim and motivates in chapter 1 that we do have such a precision in his theory. It is fixed at 60 degrees (but the exact number does not matter). So you would get a binary outcome of the Stern Gerlash experiment because the deflection is a function of the angle, now the angle is fixed and you only get a binary outcome, just as Einstein and Ehrenfest concluded. And many of the Stern Gerlach experiments follows just from this phenomena. Now the main issue is to explain why the angle is fixed and this is what Mills shows it really is for his orbit sphere model.
Now ask yourself if we have a precessing electron which is measured as spin up. if the spin did not precess, we would indeed have an issue with the Aspect experiment as a deterministic system. On the other hand if it is precessing, the same electron, although the total spin is spin up directed with an angle, it could be measured either as spin up or spin down depending on where in the phase it is measured. This violates the assumptions of aspects experiments as they assume that you never in a deterministic system can measure both spin up or both spin down and hence bust the most common interpretations of the experiment as non deterministic.
Note that this phenomena, that Mills orbit sphere satisfies, does not violate the statement of the result of the Aspect Experiment as one could interpret this behavior as super deterministic phenomena which is a notion that was determined by Bell and represent as one of the loopholes for interpreting the experiment as nature is non deterministic. The fun thing is that this property has been tried by many to find a reasonable physical model behind it and now most physicists who knows about it believes it's even weirder than assuming non locality or non determinism, but not all physicists are like that Hossenfelder.
The question remains now how to explain that the recession stabilizes around 60 degrees. Mills has an argument based on torque balance which should be valid physics whatever the angular momenta at the different axis's are, which is the difficult things to pin down here.
So in total I can't find why Mills model of the orbit sphere, which is mathematically well defined and deterministic, would not produce the result you see in the Aspect experiment and Stern Gerlash.