Hello FacePalm.exe,
After quite a bit of consulting on our end we have come to the conclusion that the issue does lie within the distance field shadows.
To that end I created a test within the project you linked second.
1.) I deleted one of the walls.
2.) I created a ton of meshes in the level. Yes, they are meshes and not painted with foliage.
3.) I then Played the game.
4.) I looked down a row of trees and noticed at the very extreme end of the row I noticed the flickering that you reported.
5.) I then went to the directional light and changed the distance of the shadows to something a little closer.
6.) This seemed to fix the issue.
7.) At a certain point the engine will have a hard time calculating shadows, especially those that are dynamic and will need to be calculated in real time.
8.) I created a video to reflect the steps I used to create this. At this point in time, this is a limitation of the calculation of shadows at certain distances.
9.) I realize that this may not be a viable solution because of the large open world dynamic you have for your game.
This is the youtube link: - YouTube
Let me know if this could possibly be a solution for you. If not you may want to consider baking your shadows on larger objects and then using dynamic lighting assigned through blueprints for your movable objects.
Thanks,