Your face 3D model may be stiff in auto-rig due to insufficient blend shapes, overly restrictive rigging parameters, or poor topology that limits natural deformation.
- **Insufficient blend shapes**: Missing key expressions (e.g., smiles, furrows) mean the rig can’t create dynamic movements. - **Overly rigid parameters**: Tight bone influences or strict settings restrict flexibility. - **Poor topology**: Uneven or too few polygons prevent smooth bending when the rig moves.
Try adding basic blend shapes (smile, frown), adjusting rig influence weights to be more flexible, or smoothing topology—many auto-rig tools have simple guides for these tweaks.