To reproduce:

1. Download attached "SerializeReference.zip" project and open in Unity
2. Select "New Some Thing" gameObject in the Project window
3. Click from the main menu BugReport > Populate Selected Some Thing
4. While "New Some Thing" gameObject is selected in Inspector expand "Element 0" and notice it has a "Left" and "Right" item
5. Open Scripts/SomeThing.cs script
6. Rename the class "RootNode" to "RootNodeNewName" and save it
7. Switch back to Unity Editor

Expected results: Renaming class names should not cause Fata loss
Actual results: Observe that the Data is gone. "Element 0" no longer shows a "Left" and "Right" item and Console outputs Error:

"Unknown managed type referenced: [Assembly-CSharp] .RootNode"

Notes:
- This issue appears on both Windows and macOS
- Could not check on Unity 2019.3.0a1 because the project becomes corrupted
- Customer copied the example snippet for the new [SerializeReference] feature from https://forum.unity.com/threads/serializereference-attribute.678868/#post-4543723
- Another Forum link: https://forum.unity.com/threads/serializereference-data-loss-when-class-name-is-changed.736874/#post-4915595

Reproduced on Unity 2019.3.0a2, 2019.3.0b3 and 2020.1.0a1