by default the model already has sliders, so re-exporting isn't needed unless you want new/different ones. if it worked beforehand but not after you changed it then there's something you're missing
I could be missing something, but have no idea what that "something" is...
download the model from itch fresh, don't modify it. does it work?
Yeah, it works just fine.
I got it working on my custom model! I had to switch the vrm version from 1.0 to 0.0, now the sliders are working as intended.