Steps to reproduce:
1. Open the attached user's project "Test Project.zip"
2. Open "UIAssets/MainDoc.uxml" in UIBuilder and a text editor
3. In UIBuilder, expand the hierarchy and compare the last three attributes of the two 'MyCustomElement' elements
4. Observe that the custom element under Beta1 has values for all three attributes
5. Observe that the custom element under Alpha1 only shows the string value
6. In the text editor, observe that there are "project://database" references for the two null values attributes of the custom element under Alpha1
7. Enter play mode and observe the two error messages in the console

Expected results: the overridden values of the Alpha1 custom element are displayed in UI Builder and accessible in runtime
Actual results: the overridden values are missing in UI Builder and return NULL in runtime

Reproducible: 6000.0.33f1, 6000.0.0a10
Could not test on 2021.3.47f1, 2022.3.55f1 due to assembly errors after downgrading

Testing Environment: Windows 11 23H2
Not reproducible on: no other environment tested