Nanite Failure

Hi guys,

i´m recently loosing my mind by using Nanite. I tried for the second time a pretty good explained tutorial to build a realistic landscape with nanite. I followed the tutorial step by step. I even reinstalled UE 5.4 and put all settings to default.

But everytime I enable Nanite and start building the data the following result comes out:

Thats with out nanite:

What do I wrong?

I found no solution to that problem on the internet. I can´t be the only one who is struggling with this issue.