Light projector either makes tiles of light or extra lines. I'm suspicious about the terrain's LOD but even if that's the case, I'm not sure how to get rid of unwanted results of projector on the terrain while having LOD enabled (I need LOD). I'm trying to make 3D GUI. Could projectors be a good solution at the first place?
If you don't use the projector to project on the terrain, but on other objects - you can just make the projector not effect it [the terrain]. Put the terrain on a layer that is excluded by the projector. On the projector component you have "Ignore Layers" layer mask that you can use to select which layers the projector is not effecting.
If you need the projector to effect the terrain - post a screenshot of how it looks, and the texture you use in the projector. Maybe there's a simple fix for it.
To fix the extra lines on my shadow projector (which is similar to the default shadow projector), I just changed my shadow texture to “Automatic Truecolor” in the format box in the default tab on the import settings for the texture. There is something about the default import of grayscale images that makes them a little messed up, I am not sure what though.