Quote -    No lights in my scene. Turn yours off?

Shouldn't be relevant. With diffuse and specular set to black, they are doing nothing except providing preview lighting.

Quote - Also, I've been rendering with indirect light quality of at least 50. Below that, there's too much mottling from the emitters to be any use in a real scene anyway. With the primitive, I'm seeing the artifact even on smaller renders.

Okay, I'll ramp up IDL quality.

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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