System does not have a parent.
A child system has no parent/child relationship with a parent system.
A serious and unexpected error has occurred, likely while changing the child system’s parent.
Because the system does not have a proper parent/child relationship to a parent system in the database, it cannot be displayed in the Workspace Explorer or other tree views. Any branch of the system hierarchy below such a system will also not be displayed in the Workspace Explorer or other tree views. The broken system and any systems and parts in the branch below the broken system are lost from view, even though they continue to exist in the database.
What You Should Do
Open the model.
Click Tools > Custom Commands.
Run the Clean Database custom command.
On the Clean Database dialog box, select the objects with this problem description.
Click Clean Now. This operation will fix all of the systems that have this problem.
Close the Clean Database dialog box.
The corrected systems will not be visible yet. The Workspace Explorer and tree views use caching that is not updated when the Clean Database command is executed. Even refreshing or reloading the workspace will not cause the corrected systems to become visible. You must close and then re-open the session before the cleaned systems become visible.
Save and exit the session.
Re-open the session.
The cleaned systems are placed in the hierarchy as children of the root. You can move them as needed.