Precompute GI produces black faces

Pictures below show it best. I have read about this both here http://forum.unity3d.com/threads/black-spots-with-precomputed-realtime-gi.349300/ and here http://forum.unity3d.com/threads/realtime-lightmap-generating-black-patches.313373/. I have Lightmap static checked for all objects as well as Generate Lightmap UVs on import. I have tried checking preserve UVs, Ignore normals, increasing the irradiance budget and quality, changing the scale of the lightmap etc... These things work to a point (they correct some objects though not all). The dark faces typically occur in shadowed areas though not all of the time - results are largely inconsistent. Does this look like a bug to anyone else?

Before Precompute GI


After Precompute GI

 

Just a shot in the dark™, but I noticed the same behavior when I was trying out different lighting configurations on some of my trees.

For me, that dark shading was caused by the Ambient Occlusion setting on the material/shader -- turning it down removed/lessened the blackening effect on areas not directly exposed to the light source.

 

Thanks for your input. I think I've figured it out and it's really pretty logical. We optimize our model by deleting extra polygons that are never seen by the user - including those on the underneath side of objects. When you run a precompute GI on the scene, some of the faces that are that in shadow appear black because the light bounces underneath the object are not calculated correctly due to the missing geometry. I have re-added all of the polygons to the underside of these porches and the GI results are now correct!