Terrain show shadow line from specific distance

HI all.

I have this strange problem where i tried to create map for my strategic game.
At specific camera distance strange shadow line appeared.

I change Camera render distance and terrain base map dist. didn’t help.
Any ideas what is causing it.

Two Q’s:

  1. Is this artifact sensitive to the size of your shadow cascades in the renderer settings?
  2. Do those lines correspond to the borders of adjacent terrain objects, or is this all in one terrain?