The Whittaker Terrain Layers are mixing or over-writing textures.
As shown very clearly in a set of pictures Here https://forum.unity.com/threads/released-mapmagic-2-infinite-procedural-land-generator.875470/page-27#post-7292620
When adding more than just a couple of graphs the layers get mixed up and the textures go awry. This is on unity 2020 With the 10.x HDRP pipeline path.
Adding Snow Plains as one of the graphs seems to sometimes clobber MULTIPLE id's It does have a few unique textures more than all the whittaker default ones. Maybe something in TerrainLayers? I am not sure what to add other than adding multiple textures eventually makes the textures "get corrupted"
There are no errors it just "goes wrong"