Minecraft: 1.17 pre3
Canvas: canvas-mc117-1.17-1.0.1578
Another mods: clothconfig 5.0.34, cullleaves 2.1.0, dynamicfps 2.0.2, entityculling 1.2.2-prerelease1, fabricapi 0.34.8, fabriczero 0.2.1.
Screenshot:

It would be helpful if you posted your logs and your shader debug folder

Is your smooth lighting set to minimum?
Does it happen after changing pipelines, or immediately after loading a world?
Does restarting mc fix it?

If possible, please provide exact steps to reproduce it reliably.

Log:
https://pastebin.com/AZJcvwfW
shader debug folder is empty
smooth light = off
restart dont fix
its after loading world
options.txt
i didn't touch options in canvas

i changed option ao shading to subtle_always but blocks are grey

if set ao shader to none this fixed

Can confirm this in 1.17 + more recent build.

Only happens when AO Shading is NORMAL and Smooth Lighting is OFF.

Just ran into this issue as well. Turning on smooth lighting and then disabling it causes other weird effects:

Additionally, while joining a world there were random black flashes in the sky (unable to reproduce again sadly). They didn't cover the whole sky, it was random areas. I had smooth lighting enabled (minimal). I'm not sure if that's related to this issue, but I'm mentioning it just in case.

Thank you for the additional reports. Both issues should be fixed now.