Large beam angles seem to cause very large "black areas" in the live views and rendering when spill lighting is enabled.

Example video: https://www.youtube.com/watch?v=0rUbB08G9Ek (Please ignore The Imitation Game in the background)

This seems to happen with any lighting fixture that has a beam angle past ~90-100º, but I haven't figured out the exact value yet. The black "area" affects everything, as though a giant black box appears as one pans and tilts around. These artifacts vanish when spill lighting is disabled. In this video I swap out the lighting fixture to show that it's not just that luminaire.