It is possible that the calculated control parameters do not bring about the desired characteristics.
Possible reasons:
Slack
Static friction
Position-dependent friction
Position-dependent rigidity and damping on spindle drives
Mechanically coupled axes (Gantry axes)
Temperature-dependent changes
Wear and tear
Aging
Process-related changes (pressure forces that are not yet in effect when tuning)
Load conditions
Non-linear kinematics
Multiple drives and motors
Interaction between multiple drives