I have created a landscape material and set it to automatically spawn grass. It all works but when you look up (I have the 3rd person pack installed) the spawned grass around you turns black, when you look back down to the ground it becomes normal. Is this because of the light? or do I have something wrong in the LandscapeGrassType or the material?
Probably eye adaptation.
Try disabling the feature to see if it changes things/makes it the same or not.
Can be a problem with Landscape layer blends. Have you created the landscape layer info for each layer already? Usually, when the layer is black, it means it doesn’t have landscape layer info created. You can create it from the plus button next to the layer in Landscape Mode → Paint.
Check these too:
https://www.reddit.com/r/unrealengine/comments/eccmb6/landscape_material_is_always_black_whatever_i_do/