I am using Standard Edition, version 16.0
I have reversed engineered model from Java. When constructing class diagram I saw that some associations were not displayed on the diagram. I tried to show them by right clicking-> Related Elements → Show Associations and got the following (see the image below). The class that is reported to be missing in the dialog is just above it.
Thank you for your post. I guess that when you reverse the Java code, you just reversed a part of it, not all classes. Therefore, when you try to visualize the relationship of a class, the related classes that weren’t reversed are found not exist, and that’s why you are asked if you want to create it.