That looks identical to the "artifacts" I see along track and road splines my current route. It is, in my case, due to using PBR textures. These textures work by changing the terrain height slightly (just a few centimetres) but it is enough to create the "shadow-like" effect you see plus another effect where the texture "overlaps" the track/road spline like the corner of a sheet of paper.
The good news is that it is easy to resolve. In my case I simply reapply the texture that is under the spline, you will probably have to "sweep" the texture brush to each side of the spline at the affected places. But, in both cases (shadow and overlap) the problem can be removed.
Peter