Dark stripes on surfaces in V-Ray when rendering to texture (baking)

Question

I am working in 3DS Max with V-Ray 3.4. I have recently been encountering strange artifacts on baked textures. Surfaces that should be flat smooth objects render with dark stripes or other unusual patterns, usually geometric. The objects affected appear to be random. One will bake just fine and another that is an instance of the first has these stripes. And once an object starts baking like this there is no going back. The only solution appears to be to remodel it from scratch (and that is not guaranteed to work either). And this behavior only occurs when baking. Normal rendering works just fine.

Things I have tested for and ruled out:

• Co-Planar surfaces
• bad UVW mapping (Tried automatic and manually unwrapping - no effect)
• bad material
• lighting problems
• bad normals
• and I've tested on multiple machines with the same results

Below is an image of what I'm talking about. The large square surface should be more or less smooth and evenly lit, but instead, there is a strange dark rectangle.

Answer 1

Solved. The issue was with V-Ray's global ambient occlusion on the GI tab. Once that was shut off everything renders fine. Interestingly, V-RayDirt maps in materials seem to be behaving just fine.

UPDATE: It appears the real root problem is deeper. This turned out to be caused by units being set to fractions instead of decimals. This can cause some values that are very small to round off to zero as the system tries to make it a fraction. In v-ray lights, the shadow bias was getting rounded to zero automatically in some cases. A zero shadow bias can produce strange results in some cases. SOLUTION: stop using fractional units and go through and fix lights with zero bias.