I am rendering a model in twinmotion and for some reason when i turn on render mode (ray tracing) my grass and pavement materials just appear as white. i am not using 3d grass, just the grass material, and two-sided geometry is checked. I used painted vegetation and that shows up, but you still see the white underneath where the grass material should be. I have messed with all the material settings and uv mapping, and nothing i find online is working. I have HDRI on as well but never had this issue. here is a photo
Have you tried using a Terrain from Vegetation to apply the grass to ? You can paint the grass area with one of the Grass Materials before applying the grass and it helps hide the white areas. As far as pavement try adjusting the tint darker.
Maybe this helps.