I was told (on the Unstable Diffusion discord, so this info might not be reliable) that even with using the same seed the results will differ if the model is running on a different GPU. This was also my experience when I couldn't reproduce the results generated by the discord's SD txt2img generating bot.

I'm not sure about the different GPU issue. But if that is an issue, the model can be made deterministic (probably compromising inference speed), by making sure the calculations are computed deterministically.

It absolutely should be reproducable, and in my experience it is.

I do tend to use the HuggingFace version though.