Here's a big pit.

• The corners of the pit aligned with chunk corners are very dark.
• Along the upper-right corner (non chunk-aligned), there's a dark spot every 16 blocks.
• At the bottom, there's a dark spot where the chunk-aligned wall crosses a chunk border.

This is in my dev instance as of here, versions of stuff:

minecraft_version=1.17
yarn_mappings=1.17+build.5
loader_version=0.11.3
fabric_version=0.34.9+1.17

modImplementation "grondag:canvas-mc117-1.17:1.0.1598"
modImplementation "grondag:frex-mc117:5.2.223"

Canvas settings are all default (uh, pretty sure).

• Happens on all render pipelines.
• Reducing the game's brightness setting makes the AO artifacts darker.