Not at all sure.
What I see is that when rendering first starts, the screen is populated with the usual dot patterns. In fact parts of the picture actually do render out enough so that pieces of the image are recognizable. But then those pieces disappear and eventually the remaining dot patterns disappear. This happened on Sunday - I saved the image I'd been working on for a few days (in T4 Beta) then tried to open it up again, only to to be met with this behavior.
It's not that big of a deal, I can pretty much recreate what I lost (I save images and incrementally save the TGD with a new name every day or two). So work wasn't totally lost