Seems like the cause is most likely my PC. (Ryzen7 1700x - GeForce GTX 1070 – Windows10), win and all drivers are up to date. After a reboot P12 rendered all volumes correct again. Maybe one of my other apps is messing with the GeForce driver.

It also could be that the windows updates are messing up something on my PC. After the update before the last one my P11 started to frequently crash. After the last win update P11 runs stable again.

It may be one of the instabilities introduced with Poser12's last iterations (V619)
I mean, I have been working on a scene with "Shades of Vanilla Skye) during 2 days, and for whatever reasons, the third day, Poser12 crashed by simply re-opening the scene, or it crashed while starting the render

For example, while I'm writing this response, Poser12, freshly opened, froze, with an empty scene,at the moment when I tried to close the program using the upper-right cross. I've filed a ticket at the support on Friday.

𝒫𝒽𝓎𝓁

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👿 Win11 on i9-13900K@5GHz, 64GB, RoG Strix B760F Gamng, Asus Tuf Gaming RTX 4070 OC Edition, 1 TB SSD, 6+4+8TB HD
👿 Mac Mini M2, Sonoma 14.6.1, 16GB, 500GB SSD
👿 Nas 10TB
👿 Poser 13 and soon 14 ❤️