Was this not fixed in 16.11.4?
I opened a Twitch stream before the game, but closed it soon after it played, and I saw artifacts at the bottom (around 21 seconds).
This was reportedly fixed in 16.11.4:
"Fixed Issues - H.264 content playback may experience playback issues on internet browsers with hardware acceleration when also running gaming applications or content."
Here's a clip from today of no other window open, but I got white blocks:
I use default RAM speed (1.625GHz), but I have a 100MHz core overclock. In the past drivers, clocking RAM faster would cause these block artifacts to appear faster.