Lightmass: multi-bounced sky lighting

I’m losing my time to try have a decent lightmass to remove this f**** lightning dark and white leak in my scene. Why is always the same problem in each versions of UE ??? My walls aren’t overcrossed, but as each versions we have always the same error with UE lightmap. In 4.18 and 4.19 preview, if i active multi light sky bounce, i have black leak on all my walls