No GI after lighmass bake

I’m having no GI after baking lightmass

for testing the image below is a new project, a static spotlight and a bsp cube in hollow mode
looks like it is only baking the direct light

I tested really high light values and diffuse boost in world settings
I’am missing something here?

edit 1:
new test this time showing the volume lighting samples
the new mesh still dark (no bounces)

edit 2:

same test on 4.7.2
looks like its working fine
diffuse boost 2

looks like the problem was with my unreal instalation.
I removed 4.8 and downloaded again and the problem is gone.