Articles that have been moved out of the world are still appearing in the World Tree as duplicate/ghost entries.
1. Have multiple articles in a world 2. Move or remove an article from the world 3. Open the World Tree panel 4. Observe the removed article still appears in the tree 5. Click the tree menu and select "Refresh" 6. Perform a hard refresh (CTRL + F5) 7. Observe the article still remains as a duplicate/ghost entry
Sometimes this happens, use the collapse tree option instead of refresh