Yesterday when I turned Zwift on, it did another update (that has happened a couple times in the past week). After the update everything was fine until I reached the waterfalls in the Road to Ruins ride. While behind the falls I started to see transparent light blue squares and rectangles that moved about about the display screen. Once past the falls, I never saw them again. What I have done is use the Zwift Insiders hack and turned off the auto-brightness command. I will see if that helps on my next Road to Ruins ride. If anyone has the same problem, I will report back after the next R2R ride.
https://zwiftinsider.com/disable-auto-brightness/
Harry