I tried uploading it and some fbx,obj versions including one with different y,x,z coordinates and I get also two errors in Mixamo. I tested Mixamo with another human design I have and it worked...must be something with the skeleton that I don't know what it is. Transforms are all ok scale1 and rotation0, normals are ok too so I have no clue to what it can be. the test was with a design that also has thin limbs like the skeleton...Sorry!
