Richard Gavin

I had this issue also, 1. no details appearring 2. Sometimes appearing in white, in long lines across the terrain.

If the detail prototypes are getting created in the inspector by the asset then,
go to the terrain, go to the details tab, RMB and edit the detail, Turn off gpu instancing, turn it back on.
Get the camera nice and close to the ground just to be sure they are there, as depending on terrain size they can
be very small.

Was driving myself a bit crazy with getting it to work and just a flick on/off of that button did it for me.
As a side note if details appear pink check the diffusion profile is being picked up.

Hope this helps.

Rocks, 2 rounds of COPs

Its probably best to do this at the rendering stage in H20 you can use the hex tile node for karma.
If you are in an early version you can build you one using mtlx nodes.