It’s a bug with the new iris drivers that were released in feb, I have the issue too. I’ve been rolling back the driver to last year’s version for months now and windows constantly re-updates it for me, sometimes two or three times a day, sometimes mid-game.
Nothing like being in p8 WSK when your screen goes blank and your driver auto-updates, crashing your game. I’ve tried disabling driver updates, tried enforcing it in the registry… nada, it still upgrades itself back to the busted version… at a rreaalllyy inconvenient time. Don’t drop anything on the ground, you’ll lose it. 
If/when your driver re-updates itself on you… just go into the game options and set ‘transparency quality’ to ultra, and the white globs will disappear.
Harrogath is the easiest place to test, half the city is missing textures and is just a white mess.