Inverted shadow / light when using Ambient Oclusion

Im relatively new to Unreal but watched hours of tutorials and searched the forums on similar issues. I set up an archviz scene and did some test renders, disabling environment light, post-processing volume, screen space AO, so that the scene is ONLY lit by a single directional light. As soon as I switch on AO in the world settings, the lights and shadwos appear to be inverted. If anyone have an idea where the problem resides here I would be super grateful.

Im using the latest versions of OSX and Unreal, and attached screens for the light and world settings used. Note that both images use exactly the same settings except for switching AO on and are displayed in Lit Only mode.

AO off

AO on