Resolved after scaling - shadows behave different (ambient occlusion)

I have a cube where the graphics look perfect with the built-in renderer.
Howerver the scaling was to small, after scaling it, all the shadows between the gameobjects (in this case the trees) disappear.

Its still with all settings set to Ultra. here are 2 snapshots, one before the scaling - one after the scaling.

I hope you can guide me in the right direction to get this solved.
is it Lighting or quality settings or ...

thanks.

original:




after scaling:

 

okay..
I think I found it, where I never expected it.

That is, when you buy something from the Asset Store, you never know, where the "trick" is hidden.

looks like it is in Post Proces Volume: Ambient Occlusion
I guess I will play arround with it a little bit