hopefully i am not sounding too pedantic in mentioning this. But LLMS are still deterministic if you're using the same prompt and seed , temp , (sometimes requires the same hardware even) etc.
For example, the result of summing a stream of floats depends on the order the floats arrive in, and that order can change depending on what’s in your CPU cache when you start a computation, on whether something else running on your system such as a timer interrupt evicts something from cache during a computation, etc.
If you’re running on your GPU, even if the behavior of your GPU is 100% predictable (I wouldn’t know of that’s true on modern hardware, but my guess is it isn’t) anything that also uses the GPU can change things.