Steps to reproduce:

1. Open the attached project
2. Open the SampleScene
3. Create a new UI Document object in the Hierarchy
4. Assign the test.uxml asset to the newly created UI document object
5. Observe that the UI Document object can be fully expanded to display its Visual Elements
6. Open the test.uxml asset in the UI Builder window
7. Make any changes to the document (for instance, add a new label element)
8. Try expanding the UI Document object in the Hierarchy window again

Actual results: The UI Document object does not expand, or the expanded elements flicker for a brief moment

Expected results: The UI Document can be fully expanded

Reproducible with versions: 6000.3.0a5, 6000.3.1f1, 6000.4.0b1, 6000.5.0a3

Not reproducible with versions: 6000.3.0a3, 6000.3.0a4

Can’t test with versions: 6000.0.63f1, 6000.2.14f1, 6000.3.0a2 (UI Authoring Hierarchy integration was not yet available)

Tested on (OS): Ubuntu 24.04, macOS 26.1