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.