We are upgrading our project to 4D v12 and our QPix plugin stopped showing us a preview of the image we are about to take. The image capture works just fine; the only problem is that the preview simply shows a white screen.
If I select the "Video Settings..." button I get a screen with a preview, so I know that it should be possible to get the preview.
This is a longshot; if you need any more information I can provide it.
I heard back from Escape Tech Support and they claim that the issue is a bug in 4D v12. They are hoping for a fix in 4D v12.1.