Pic:
https://snapr.pw/i/15ecf00182.png
As you can see, the tree’s (instanced foliage) static shadow is disappearing the nearer it is to the camera, this appears to correspond with CSM’s dynamic shadow distance. The foliage/trees are set to only cast static shadows and no dynamic shadows.
This question: Cascaded Shadow Maps and Static Shadows - Rendering - Unreal Engine Forums
seems to have the same problem.
The other issue is that regardless of distance the trees seem to never self-shadow.