my skylight does not create realistic shadows

in the red boxes, there should be shadow, but there isn’t. i use a lightmass portal: ← click link for my image!

what i tried:
higher light map resolution.
using a default cube from ue4 as a floor. still the skylight doesnt create shadows on the default cube (statismesh)
skylight and sun do cast shadows.
i changed lightmass settings.
and perhaps other things, don’t remember.