Inside the foliage tool, QA-Foliage-CullDistance has Static mobility so its shadows are baked into the shadowmaps and will always be rendered. Changing the mobility to Movable, setting Cast Dynamic Shadow and rebuilding lighting restores the behavior
Watching GIF displayed in test case, the shadows disappear with the meshes.
Result: Procedural Foliage Instances are no longer visible but their shadows remain, no matter the distance
Expected: Shadows to disappear with mesh
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-34988 in the post.