This seems to be an issue with non-full blocks like stairs, slabs, and even powder snow.
With stairs and slabs, though, it particularly occurs on the faces of the blocks that can be in direct contact with other blocks... Like the sides of a slab or stair, the top of a top slab, the bottom of a bottom slab... etc.
This is easiest to see with brightly-colored blocks, like quartz.
Affects 1.19.81
Though I can only get it to happen with the left/right sides of stair blocks.