I've encountered NAN/INF pixels with sep 12 build. Didn't do anything fancy, just played with SSS material. At some point NAN pixels occur and from there on, it was impossible to get rid of it. I've tried to override basic material, changed lighting, even hide all geometry, but those pixels remained. Eventually i saved scene under different name, restarted max, opened that same scene and NAN's were gone. I've tried hard to make to show them back, but no luck.