Dead Black Shadow with displacement

[reism]

Hi,

I just find the unusual dead black shadow with displacement.
As the photo attached below, I have applied displacementt to the bottom box and set the height as 10. And the models above will give the unusual black shadows. It will not disappear unless I set the height to 0.
Any solution to this? Thank you.

[aoktar]

Check with different ray-epsilon values