When a 3D model is scaled (especially non-uniformly, like stretching one axis), its normals—vectors that define surface direction—can misalign, causing faces to appear hidden or shaded incorrectly.
Normals tell renderers how light interacts with surfaces and distinguish a face’s front (visible) vs. back (hidden) side. If scaling distorts normals, the renderer might misclassify faces, making parts of the model seem hidden.
To fix this, recalculate normals in your 3D software (e.g., Blender’s “Recalculate Normals” or Maya’s “Normalize”) after scaling. This realigns normals with the model’s new shape, restoring visibility.