I’ve created your default 3rd person blueprint project, created some landscape, made a few little mountains and quited it. Then I added Landscape Mountains feature pack and dragged a rock to scene. And as I said it took a while to load shaders. Then I applied one of grass materials from same assets to landscape and it froze my computer.
I’m not saying that this might happen on any computer, maybe it’s specifically with my hardware, though I have no idea what could cause crash of whole pc.