Strange & Wrong Shadows or AO

Hi All - I have an other new problem…

Below I show two pictures of a staircase.

The first picture shows a steeper view from below up against the podium ceiling - Here everything is ok so far!

The second picture shows the same view, but the viewing angle is a bit flatter. Suddenly a strange false shadow(?) appears and spoils the scene!
The flatter my viewing angle gets, the bigger and even darker this « shadow bug » will be …

There is nothing in the model which could cause this shadow. Also, I’ve observed that this disappears when I put all AO settings to 0.

  • So I suppose that the AO module causes this bug (?). Finally, I rendered the scene as PSD and this « shadow bug » gets displayed on the AO layer actually.

Any help is urgently desired here - thanks!