Black patches in lightmap

Hi, I am facing a problem when I lightmap my scene

Here’s a screenshot:

Here you can see those dark black shadows under trees however these cubes are totally same (Duplicated) but I don’t know why these patches are made onto some of the cubes after lightmapping. Can someone share a fix for this? Or guide me why is this happening?

NOTE: Generate Lightmap UVs is checked and applied for these cubes.

HERE ARE IMPORT SETTINGS FOR THESE CUBES.

AND HERE ARE MY LIGHTING SETTINGS.

ANY FIX FOR THIS?

Enable double sided GI in your tree canopy material settings.

Double Sided GI only works with Progressive CPU lightmapping but I need to use Enlighten. Anything for that? Or any other solution/workaround?