When using instanced meshes in a Blueprint or in foliage tool the indirect lighting cache will not correctly light these meshes.
I've include a sample project with map to demonstrate what the licensee is seeing along with a gif they provided that demonstrates this as well.
In the map I've included the foliage type that can be painted to reproduce and set up a BP that is with an Instanced mesh. This can be easily moved between the RED, BLUE, and Darkened middle areas as this will produce the same result. If you look at the volume samples these are well spaced as well, but do no honor the location of the instances.
Sample Project is using 4.10
1. Open UE4
2. setup a simple scene with static lighting only
3. Place any colored light that is static.
4. Place a mesh in the foliage tool that can be painted
5. Disable static lighting for the instanced foliage mesh
6. Paint meshes around the scene.
Results: It looks like a single central point is being grabbed for all instances to use with the indirect lighting cache. This causes mesh instances to not be correctly lit, even if a indirect light sample does not directly come in contact with the instances.
Expected: The instances should be lit correctly by their corresponding indirect lighting cache sample.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-20029 in the post.