Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Make sure Hierarchy V2 is enabled
3. Create a new Tree GameObject (GameObject > 3D Object > Tree)
4. Delete the "Assets/Tree.prefab" prefab
5. Repeat step 2
6. Observe the Hierarchy V2 window
7. Select all Tree GameObjects in the Hierarchy V2 window
8. Delete the selected Tree GameObjects
9. Repeat step 6
10. Right-click any of the leftover Tree GameObjects in the Hierarchy V2 window
11. Observe the Console window

Actual results: Multiple Trees are created after deleting a Tree Prefab, some Tree GameObjects are impossible to delete from the Hierarchy V2 window, and a "NullReferenceException: Object reference not set to an instance of an object" error is thrown when right clicking one of the un-deleted Tree GameObjects

Expected results: Only one Tree GameObject is created upon creation, all the Tree GameObjects can be deleted from the Hierarchy V2 window and no errors are thrown when right-clicking a Tree GameObject

Reproducible with versions: 6000.3.4f1, 6000.4.0b3, 6000.5.0a4

Can’t test with versions: 6000.0.65f1 (due to no Hierarchy V2)

Tested on (OS): MacOS Silicon Tahoe 26.1