Hi! I have this issue of having an additional material I can't seem to figure out how to remove when I upload my .obj file (exported from Blender) into sketchfab. It started out with loading my .obj file into Mudbox. Mudbox identified that there was a non-manifold problem (as indicated by big red arrows streaking across from where I X-mirrored my mesh). I attempted to correct this by deleting the faces associated where Mudbox identified the problem. Then I found out that my mesh has a second skin after I recreated the faces along the mirrored portion. I deleted the second layer of overlapping faces which I have absolutely no idea of how it conjured itself into existence. I then merged the faces that needed to be reconnected. I then exported my mesh into Mudbox and I created the texture for the model with no hints of any issue. I uploaded my .obj mesh on to sketchfab and I see that there are two materials instead of one. One material outlines the middle section and arms, the other material outlines the vest (materials named: Material_NONE, and Material). I know I am doing something very wrong, but I have no idea how to fix this issue.
Help would be very appreciated from experts!