Your blend shapes 3D model is deforming usually due to incorrect weight painting, conflicting shape key interactions, or mesh topology issues that prevent smooth vertex movement.
Weight painting errors happen when vertices get too much or too little influence from a shape key, causing uneven, unnatural deformation.
Conflicting shape keys occur when target shapes don’t align with the base mesh’s structure, leading to unexpected warping or overlaps.
Poor mesh topology—like non-manifold edges or uneven edge loops—breaks how vertices move together, resulting in jagged or broken deformations.
To fix it, check weight maps in your software (e.g., Blender’s Weight Paint mode) for unevenness or test shape keys one at a time to isolate the problem without reworking the whole model.