I use Unreal version 4.26.2.
I asked a question on the answer hub, but I can’t find a solution.
Today I reproduced the same problem with WaterPlugin’s WaterTestMap.
Increasing the DistanceFieldShadowDistance(or Dynamic ShadowDistance MovableLight distance) for directional lights creates unknown shadows.
For reference, I set the DistanceFieldShadow distance to 80000.