I've had this problem a few times, and I just don't understand what's causing it. In these three shots, all that is changed is that the camera is pulled further back in each shot. In each image there are nasty black speckles, but the area affected increases as I move the camera. Weirder still, the speckles cover the back wall and objects on it, but not the sky viewed through the gap in the wall, nor the side walls. A bit of the floor is affected. The lighting is just a few standard point lights, no soft shadows or anything like that. As I move the camera around, or the room around, the problem gets better or worse in ways that I don't follow. What IS causing this?