TGD attached, what are these weird black areas?

[elipsis1]

I assume these came from the redirect shader, weird black shadow areas or pits?  They don't look natural to me though.

Probably more Noob error, just trying things out...

[Dune]

Indeed, your displacement in the redirect PF is way too extreme. Better to keep displacement less than the smallest size, so 30/3000/30 and displacement 25 or so, or accordingly, depending on your terrain.