Shadow artifacts on engine launch

Hello everyone!
I currently have a problem with my project that I have no idea how to address.
As soon as I open the project in my editor, weird shadow artifacts appear in the areas of my low-poly meshes that are not directly hit by sunlight (1). What’s even weirder is that when I get closer with the camera, those artifacts disappear (2), and don’t return visible until I close and re-open the editor.

As you may guess, this is not a terrible problem, but it has been really bugging me for quite a while. Any clue on how to fix this annoyance?

Some data I think may be useful:

  • The sun is set to stationary
  • These black lines appear only on the edges of polygons lighted by indirect lighting
  • Lightmaps are fine and correctly scaled (light blue to green in the visualizer)
  • Once disappeared, everything looks fine even on long distances