Now you're making me wonder if you accidentally gave a bad clue in the beginning, and as a result we've all gone in the wrong direction.

You said "I seem to get a patch of grey in the top left corner.  Since I'm using a quad core processor I have the threads set to 4.  So in the lower left quadrant I also have a patch of grey in its upper left corner."

Now you show us a render, but you only let us see what looks like the first two buckets from each renderer. You really can't expect us to figure it out with no knowledge of your relative camera position  with respect to props and figures, no knowledge of those props and figures, and no knowledge of your camera settings, and on top of that, you won't show us the picture.

What if it isn't about the upper left corner, but rather its about something else.

Since you're stuck, give us a full render, and the other info, and let us judge.

Off the top of my head, I'd suggest you adjust your camera "Hither" setting, since you may be too close to some props.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)