I don’t know if this is a bug or if my settings are wrong, but I’m having the following issue:
Foliage painted with the foliage tool stops receiving shadows from a light source if the light source is higher in the world than the instanced foliage actor.
Here we have a point light, some foliage painted with the foliage tool and a static mesh, highlighted with the arrow. With the point light at a height of 204 cm there is no problem.
Then watch what happens if the light is moved up one cm:
The foliage stops receiving shadows from the point light, while the static mesh still behaves normally.