Steps to reproduce:
1. Open the attached user's project "1339919_FindPropertyRelative.zip"
2. Click on Collection under "Assets/1339919/", observe its List<Element> contains an ElementA and an ElementB
3. Deselect Collection
4. Drag "Assets/1339919/Asmdef/Runtime.asmdef" into "Assets/1339919/Scripts"
5. Drag "Assets/1339919/Asmdef/Editor/Editor.asmdef" into "Assets/1339919/Scripts/Editor"
6. Let Unity recompile
7. Select Collection
8. Observe error. "Unknown managed type ElementA"
Reproducible on: 2020.3.38f1
Not reproducible on: 2021.3.8f1, 2022.1.15f1, 2022.2.0b8, 2023.1.0a11
Notes:
- In the Assets folder is a ScriptableObject called Collection. This contains a List<Element>, decorated with [SerializeReference] attribute
- Element is an abstract base object with two inheritors, ElementA and ElementB, which also define their own data
- There is a custom PropertyDrawer called ElementDrawer which runs on both ElementA and ElementB
- There is a custom Editor for the Collection, which is not important and simply allows us to add ElementA and ElementB objects to the List<Element>