It seems that PC can get "tired" after it has been in the swirling vessel for a while. Typically a little fresh PC is added to the vessel, but after a while (perhaps 1k or so bullets), something goes awry with the PC. I think what's happening is that some elements are more attracted to the bullet via static than others. Perhaps leaving "dregs" in the mix. The dregs accumulate and change the mix, perhaps. I don't know.
This bullet was swirled in a bowl that had been used for probably more than 1k bullets, fresh PC was added as needed. Snapware container and black BBs. Note that it is well covered, but very thin. The thicker "normal" pigment is dispersed. It is so thin that my fingernail can scratch it even though it passes the smash test. The areas with normal thickness and pigment are tough like usual for PC.
So that PC and BBs got dumped. The fresh batch of PC and back to normal.
Both examples are a mix of Smoke's Yellow-Green with a little Signal Blue and Jet Black.
After seeing this a few times, it's clear that at some point "mixing the new gas with the old gas" makes for less desirable results.