Nearly every time I export a character into blender & switch over to cycles, I get shading artifact issues like this. It's not caused by the materials either, it has something to do with the mesh from character creator. I will add a link to the mesh file.
I use auto smooth & smooth Normal's, I've tried turning them off, nothing I do seems to help, even a Subdivision Surface turned up to 4 doesn't help.
Mesh - https://www.mediafire.com/file/utxk85s7np1ck44/character.fbx/file
75% of original size (was 668x19) - Click to enlarge75% of original size (was 668x19) - Click to enlarge

Here is what it looks like with 2 subdivions from a subdivision modifier.
75% of original size (was 668x19) - Click to enlarge