Unreal not generating Volumetric light samples inside LightmassImportanceVolume

I have a lightmass importance volume inside a large closed black box and Unreal doesn’t seem to generate any Volumetric light samples, only the default, way too spaced out samples.
All lights you see are stationary, cast shadows, and all static meshes are set to static & cast shadows.

Does anyone have an idea why this might be happening?

The problem was placing this box below a landscape which seems to prevent any light samples to spawn. Fixed by moving this to another part of the map