That is probably because the diagram's (virtual) document bounds is too narrow.
Because the layout needs to work with virtual nodes rather than real Nodes, you'll note that there is a computeDocumentBounds method that is called at the end of the layout in order to set the Diagram.fixedBounds. Note how that method depends on the Rect that is saved on the data, not on the node's GraphObject.actualBounds.
But if the size (height or width) is not an accurate estimate of the actual bounds, the diagram's document bounds will be wrong.
So: did you update the statement:
//!!!???@@@ this needs to be customized to account for your chosen Node template
d.bounds = new go.Rect(0, 0, 70, 20);
to match the GraphObject.actualBounds that your Nodes really have?