Sorry… sounds dumb to ask but didn’t see you mention it. In the data connection did you map the cells of the expected return data size to the internal spreadsheet?
Also after adding the WSDL it populated the Web Service URL. Grab that URL and run it into a web browser and try to get a return of the data to make sure that piece is working correctly.
Is the dashboard always launched while you are authenticated within the domain? Do you launch it externally?