*Steps to reproduce:*
# Open a Unity Project
# In the Project Window, create a new Panel Settings asset via Create > UI Toolkit > Panel Settings Asset
# In the Project Window, create a new UI Document via Create > UI Toolkit > UI Document
# Open the UI Document in UI Builder (double-click on the asset) and add one or more visible element/s to it (e.g. drag a button from the library to the hierarchy)
# Save and then close UI Builder
# Add an empty GameObject to the Scene via GameObject > Create Empty
# Select the new GameObject
# Add a UI Document component to the GameObject
# Assign your created UI Document as the Source Asset in the component
# Assign your created Panel Settings Asset as the Panel Settings in the component
# Observe the Game view

*Actual results:* The created UI does not display straight away. You have to either have the editor refresh by changing another setting (e.g. Sort Order) or enter playmode, to get the UI to display in Game view.

*Expected results:* The created UI displays straight away.

If you assign the Panel Settings before the Source Asset then this is how it works (the bug does not occur).

*Reproducible with versions:* 6000.1.0a4, 6000.0.28f1, 2022.3.53f1, 2021.3.45f1

*Not reproducible with versions:* - 

*Can’t test with versions:* - 

*Tested on (OS):* MacOS Sonoma 14.6.1

*Notes:* 
* This bug was a particular pain point as I thought I had broken the UI in some way, or that it had not been setup correctly, when it didn't display at first.