Suddenly non-deterministic

[fildred13]

I've been happily using stable-diffusion-webui for over a year now, and suddenly in the last few days I started to notice that my outputs are no longer deterministic. I don't use --xformers, so I'm used to every generation being perfectly deterministic: identical inputs in, you get an identical, deterministic output out. I've been able to reproduce generations from the earliest days with this technique, but now even two back to back generations aren't exactly identical.

I uninstalled all third party extensions, but still the issue persists.

Anyone have any idea what else I can try to solve the issue? I assume it isn't an actual bug, or more people would be complaining about it.

I've tried everything that I can think of. Threads like this don't really apply to me, because I'm having trouble with back-to-back generations without touching any settings, not with replicating gens from days/weeks ago.

[fildred13]

I just tried a completely fresh install of stable-diffusion-webui. Issue is just as bad on a clean install with a freshly downloaded, vanilla sd1.5 model.

[fildred13]

I figured it out.

The Token Merge Ratio and high res fix token merge settings were set to 0.2 instead of 0 (off). I had no idea that setting could cause non-determinism. Disabled back to 0, and things became instantly deterministic again.