Thank you for answering me so quickly!
I've cleared normal and added many times but it seems nothing changes
75% of original size (was 672x19) - Click to enlargeCleared
75% of original size (was 672x19) - Click to enlargeAdded
I've exported in Fbx format from MD but also tried with obj with the same settings that you have
75% of original size (was 672x19) - Click to enlargeThe autosmooth in CC doesn't change
75% of original size (was 672x19) - Click to enlargeI'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
75% of original size (was 672x19) - Click to enlargeSoft shadow reduced quality
75% of original size (was 672x19) - Click to enlargeSoft 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