I was copying over an existing prefab from another project to prepare a bug-report for a different issue, when I ran into this one. The prefab that I copied into the provided project has various missing scripts, because I didn't copy them. Unfortunately, I'm unable to modify the prefab, because if I remove objects, it displays the following error message: ... leaving the prefab edit mode does not save the changes. Spoiler: Video Reproduce Open user provided project Select Assets/Prefabs/Prop_FloorLamp Click "Open Prefab" in Inspector Right-click the "Billboard" GameObject and choose "Delete" Actual Observe the editor outputs an error message continuously. Expected The object gets removed without error messages and those changes are saved. Side Note It would be very useful if the error message contains the name of the affected gameobject.