Diagram does not refresh after adding new link

I have an issue that a new link does not appear in the diagram although it is added to the model.
When I move one of the objects in the diagram, the link appears.
I tried the UpdateLayout() method on the diagram but it didn’t help.

Did you make all of your model/data changes inside a transaction?

FYI, UIElement.UpdateLayout has nothing to do with GoXam.

Yes, the changes are made inside a transaction.

Then I have no idea what the problem might be.

Could you tell me how to reproduce the problem?