Greetings @AlienRenders
I’ve saw this happen a few times. I actually had a post stored that someone in the community tossed a video together with possible fixes for this specific type of issue. You’ll have to scroll down toward the bottom of this thread to find the post. But, I’d check that out first. Let me know if you get working! (The link to the thread is Landscape Material turns completely Black after Updating project from 5.1 - #24 by Akio_Kami)