For a locked shapekey, a SculptSession's orig_cos / deform_cos / deform_imats are not initialized (they only are when deform_modifiers_active is true -- this in turn is only true for shapekeys if they are //not// locked [and for deforming modifiers of course]) We can just update that keyblock with sculpt_update_keyblock() in case of a locked shapekey Maniphest Tasks: T79622 Differential Revision: https://developer.blender.org/D8499