Issue: Completely inverted light / shadow when switching on Ambient Occlusion

Dear Forum. I’m relatively new to Unreal but watched hours of tutorials and managed to setup my archviz scene. I disabled all environment light, screen space AO and post processing, the scene is only lit by a single directional light. As soon as I switch on AO in the world settings and build the light, the directional light appears to cast a black light and objects hit by it cast illumination on the floor instead of shadows.
See attached screens, displayed in the Lit Only mode. im using Unreal on OSX, both updated to the newest versions. I searched the forums but have not found similar issues. I would be super thankful if someone has any ideas on that problem.