...cleared custom split normals data...

Are you sure? Blender shcreenshoot kind of indicates that it's not cleared.

Try Auto Smooth in CC: Mesh > Edit Normals from the menu. Set relatively high angle, like 180 (you do not need any sharp edges there).

Also, how did you export from MD?
Those are optimal settings to save you from all kind of problems:




Finally, Soft Shadow on certain light schemes in CC gives weird shading artifacts.
Lower it down and see if it does change anything.
(Shadow Bias and Resolution might also affect that)

Thank you for answering me so quickly!
I've cleared normal and added many times but it seems nothing changes

Cleared

Added 
I've exported in Fbx format from MD but also tried with obj with the same settings that you have

The autosmooth in CC doesn't change 

I've tried the light settings that you suggested me and something changes a little bit but of course it loses quality and seem that the best result is to switch off the soft shadow

Soft shadow reduced quality

Soft shadow switched off
it seems that the shadows improve the situation a bit at the expense of quality.
However, I don't know if it's resolved or it's like we've put some sort of patch on it...but do you think it depends on the geometry or is it purely related to the lighting?
Thank you for your support