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Aren't these models non-deterministic by nature?

no, they run on computers. anything that happens in a computer can be made reproducible

I'm not sure. Googling for "gpu non-determinism" and reading around the results seems to indicate that GPUs are often not deterministic.

I don't know why, but it is easy to imagine a scenario where non-determinism makes sense. For example the computer could say "I am supposed to do this floating point division. Let's see ... my very exact FP-Division unit is pretty hot at the moment. 82°C. Let's pass this calculation to the slightly less exact FP-Division unit then".

cpus can be nondeterministic as well, generally because of race conditions between different cores, and as i understand it, that's what happens with gpus too, just more often because there are more cores

i think the kind of scenario you're describing does not occur in commercially sold hardware, because it poses problems not only for customers but also for verification engineers at the design house. also, in the specific case of floating-point division, it would violate the ieee-754 standard. it might happen in an experimental academic project

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