Hi @Krzysztof.N ,
I was testing in a very basic scene for a bug in CPU lightmass and I noticed some things when making a new test with Lumen enabled:
Strange artifacts appears around objects when using ligth sources with a source radius + ray traces shadows (look at the left edge of the cube):
A workaround could be to use virtual shadows even if they are much more limited that RT ones, but they are also quite glitchy. Look at the little blocks in the last wall:
Regards