Question Movable shadow edge in the terrain

Hi!

I have a problem that I can't explain. Just call it "Movable shadow edge in the terrain".

When I hover over the terrain the edge has disappeared. When I get closer to the terrain, there is a circular coloured difference in the terrain. The closer I get, the bigger it becomes.

When I am standing on the terrain, it is about 300 m away.

I also have the same effect in the editor when I zoom in and out. Apparently bias and normal bias have a large effect on the circle, but I have not found a value that removes the circle. I have also tested cascades and shadow range.

Can anyone tell me what this is?

 

Doesn't anyone have any ideas?^^