Shading Artefacts/Corruption on Mesh

Description

In the course of editing a mesh in Blender, surfaces may appear to be incorrectly shaded [1] making it difficult to determine an objects structure [2], even with wireframe overlay visible and/or Sharp edges/Edge Split being enabled. Meshes often appear to be inverted or somehow corrupted even though, on inspection, it appears that are no non-manifold or loose floating vertices, edges or faces or other structural issues causing the object to shade poorly in Material Preview or Rendered display modes (with or without lighting).

Shading artefacts [1] on a mesh making it difficult to discern structure [2], which also seemingly ignores Sharp edges.

Solution

Assuming there aren’t any physical issues with the mesh, no non-manifold, internal or other errant structures hidden inside the mesh, the problem is likely due to ‘bad’ vertex normal data being present on the mesh – vertex normals that are effectively pointing in the wrong direction. To remove or reset this data, with mesh selected, in Object Data Properties [3], expend Geometry Data [4] and then simply click the Clear Custom Split Normals Data button [5] bottom of the section. The mesh should reset in the 3D Viewport showing vertex normals correctly relative to the object as it is in its raw form with smoothing based on whether or not edges have been marked Sharp or split by angle.

Image-top: bad mesh normals are likely causing issues so in Object Data Properties [3] access Geometry Data [4] and click the Clear Custom Split Normals Data button [5]. Image-bottom: this removes the errant data, effectively resetting to the mesh to its raw, natural state.