If you include center points in the model for any of the responses, the Response Optimizer does not fit a continuous response surface. As a result, the Response Optimizer considers only the low and high levels of each factor and the center point as candidates for the optimum.
On the response optimization plot, the only points you can move to interactively are the corner points (with each factor at either the low or high setting) and the center point (all factors at their midpoint). If you move one factor to its midpoint, all other factors will also move to their midpoints. If you move one factor away from its midpoint, all others will move with it and in the same direction. Before moving to the center point, you might want to save the current factor setting.
If your final model requires a center point term because curvature exists, you might want to add axial points to your design to make it into a response surface design. Response surface designs are capable of modeling the curvature along the entire range of your factors; factorial designs cannot be used to model curvature along the entire range of the factors.