This review checks that packages, classes, associations, use cases, dependencies and specializations appear on at least one diagram.

This commonly occurs when someone selects Delete instead of Delete from Model.

One of the main advantages of using a visual modeling tool is that they provide representations of how model elements relate to each other.

If model elements do not appear on diagrams then this primary benefit is lost.

Delete the model element or use the element on a diagram (creating a new diagram if necessary).