Unity calculates “deltaNormals[]” incorrectly when a mesh has imported normals and blend shapes, specifically with FBX-imported models, where Normals are set to Import and Blend Shape Normals are set to Calculate. Currently, Unity calculates the delta between the imported rest normal and a blend normal generated using ModelImporterNormalCalculationMode and ModelImporterNormalSmoothingSource. The user suggests this is mathematically wrong - the delta should instead be calculated between the calculated blendshape normal and a new rest pose normal generated using the same CalculationMode/SmoothingSource as the blend normals.
To the user, this means models using imported normals cannot use blend shapes without either disabling normals (not feasible) or producing visible artifacts, often on character faces.
Note: Not reproduced by CQA