Visio's Drawing Explorer is a useful tool for analysing the content of a Visio drawing, and can identify issues that may otherwise be hidden or difficult to address.
You may notice that there are shapes listed that aren't apparent on the drawing (and there's nothing behind the Drawing Explorer window).
The 'Info' and 'Hyperlink circle 1' shapes are hidden behind others, and the 'Dynamic connector.35' shape has zero dimensions.
Connectors that aren't glued to other shapes at each of their ends are usually identified as non-Triaster shapes.
A glued end is depicted by a red square, an unglued end by a green one (or blue, depending on the version of Visio). The connector shape has to be selected for this to be evident. If a connection isn't glued, it won't be recognised by Process Navigator, and so neither will a shape's position within the flow of the map. In this example, the final Deliverable won't be recognised as an output of the process map, although visually it's obvious that it should be.
These are all examples of observations made on real maps, and Drawing Explorer has been a valuable tool in addressing them.