Why does GPU skinning cause mesh spikes?

Development Character & Animation
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1

I’m getting some severe mesh spikes that go away when I check the CPU skinning box in the Character->Advanced tab. That is the only difference between the two attached images.

What is happening? I checked the weight painting and it looks ok to me. I tried moving the mesh via the root bone in blender to check for unweighted vertices, but I didn’t see any tearing occur.

2

Heading there, a bit late, just a guess :
GPU probably clamp max skinning weight count of each vertex to 4, 8 or such a static value. If your skinning setup has more than that, it will probably be clamped (and maybe not renormalized), leading to unnormalized vertices which would lead to spikes / holes