Cause: The app was using the page logical id. to access the current dashboard instead of the persistent id.
Consequence: Once cloned, the app was trying to retrieve without any success the current panel status from the original workspace.
Fix: Get the cloned dashboard by its persistent identifier and also clone all the KPI referred by the dashboard panels.
Result: The workspace and all its KPI panels are cloned succesfully. You can change the cloned workspace without affecting the original one.