One cannot scroll the diagram until the diagram and its Panel have been fully initialized, until the nodes and links have been realized, and until the initial layout has completed, ensuring that all nodes have locations. Rather than calling DiagramPanel.CenterPart in an InitialLayoutCompleted event handler, you can just set this property to refer to some data, and DiagramPanel.OnInitialLayoutCompleted will center the node for you.
Note that if you set both this property and CenteredNodeData to different data, the latter will take precedence.