Shadows detached from the objects

Dear All,
I am new to the forum. Thank you very much in advance for your help!

I have some issues with the shadows of objects when rendering: it looks like the objects are always detached from the ground, so that the shadows are detached from the objects.
Please, find below an example (the issue is very visible in the area within the red circle).

I apologise for the naif question: I just started working on it!

Thank you very very much,

maybe working too far from world origin?

Or groundplane is lower than you thought it is?