It happens in both build and play modes. The lights are flickering or flashing. Sometimes so brightly I thought there must be a searchlight or something like that revolving around the scene. Also, the shadows and dark areas are much darker now than before downloading the update. Another thing I just noticed, sometimes four red squares appear about a third of the way down from the top and about a third of the way inside from the right edge of the screen.
This all just started a couple of days ago. Before then, none of this was going on.
With this problem, and my problem with Riverview discussed in another thread, I might try uninstalling the game and then doing a clean reinstall. That's probably the next step. I might refuse the update too.
If anyone has a solution or any information on this problem I would appreciate hearing it.