How to reproduce:
1. Download the user-submitted package(PrefabTestPackage.unitypackage)
2. Create a new Unity project with one of the versions, marked as 'Not reproducible'
3. Import the package
4. Open the Assets\GUI\Controls\BasePrefabs\EscapeMenuPrefabs\NewSaveSlot.prefab
5. Note the order of the prefab hierarchy(UITab is in the 3rd position)
6. Close the project and open it in one of the versions, marked as 'Reproducible'
7. Open the Assets\GUI\Controls\BasePrefabs\EscapeMenuPrefabs\NewSaveSlot.prefab again
8. Note the order of the prefab hierarchy

Expected result: hierarchy order remains the same(UITab is in the 3rd position)
Actual result: hierarchy order has changed(UITab is in the 5th position)

Reproducible with: 2018.4.14f1, 2018.4.16f1, 2019.2.14f1, 2019.2.19f1, 2019.3.0f1, 2019.3.0f6, 2020.1.0a11, 2020.1.0a20
Not reproducible with: 2018.4.13f1, 2019.2.0a1, 2019.2.13f1, 2019.3.0a1, 2019.3.0b12, 2020.1.0a1, 2020.1.0a10
Could not test with: 2017.4.36f1(Old prefab system is used)