Dispersion like artefacts from directional light when using CPU lightmass

Hey there, I`m using UE4.27.2 and have faced with such a problem. When I bake light using CPU(AMD Ryzen 7) I get very strange result, like the light coming from the source(Directional light) is splitting into the sepparate rays. The scene consists of default cubes (with default material), directional light, skylight and sky sphere. And what is more interesting I have tried the same scene in UE4.26 and got the same result. I have already tried to reinstal my Unreal dut unsuccessfuly. Does anyone know what is the problem?