I joined 2 meshes together, adding eye socket to the stalk for the eye on a crayfish. It almost looks like a ghost set of polys are making a translucent layer over the regular polys. The polys above the join edge are shinier and darker and I've tried to reset the material and that didn't help. I deleted a couple of rows of ploys and rebuilt it and the shiny just comes back. Ctrl L selects the whole model so the meshes are joined. The first picture is what happened when I tried adding a subdivision modifier.
two things could have happened, when joining the meshes the normals were not correct, in edit mode, select the entire mesh and press shift+n to recalculate the normals. If that doesn't work you may have duplicate faces, in edit mode again select the entire mesh and press the m key, in the dialog select "by distance" to join the overlapping duplicate faces.