Lol anybody remember wrothgar on release. Good ol orsinium

I had this very often before Elsweyr too. It’s back again with a vengeance, especially in crowded keep fights.

this happens usually when you get high ping and your running around. Then if you go far enough you'll usually be greeted by exactly what you see there. It usually only covers a small area of the map that hasn't loaded in yet, if you try to pass it you'll either be stuck running in place or you're game will freeze or you'll simply fall through the world. It's been a thing since the game was in it's early stages, nothing much you can do.

Edit:
If you want my recommendation then whenever you are greeted by that, simply wait until it goes away. It shouldn't take too long.