That is caused by the PBR textures. PBR textures have a height component in them that causes the textures to raise or sometimes lower the terrain and bury over tracks and roads.
There are two ways to fix this.
1) Get the texture and spread it wider to smooth out the area.
2) Turn down the shaders to Basic - the new level that used to be Standard.
PBR textures don't mix well with older 2d textures and cause the older textures to float on top like duckweed or oatmeal on water. By turning off the 3d-effect, you can use both textures together and avoid the jellyfish guts and crawling textures you'll see when you drive along steep sloped areas.