Thanks.

I've tried this with depth-map shadows as well as raytraced lights, so not sure what to do.

I don't understand why the custom morph is doing this, there's nothing extreme. Not sure how to correct polygons that have become concave (which sounds like a bug in the renderer in any case). Hope I don't have to go back to the drawing board altogether with the morph. :-

Hm. I think for a lark I'm gonna see how this renders in DAZ Studio - see if its render engine generates the same artifacts as Firefly.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3