Mesh looks OK in wireframe but shading is distorted Imported an OBJ file in Blender 2.91.0. Mesh looks OK in wireframe view and exports OK to other s/ware but weird in all shaded viewport views. Example included shows object Shaded Flat. All surfaces are concaved. A recurring issue for me. Checked normals are OK, checked no modifiers on the object apart from a collision modifier. Searched the net.  Any ideas?
Answer provided by Nathan. Solution was to clear custom split normals in Object Data Properties/Geometry Data.