How to reproduce:
1. Open the “IN-97116.zip“ project
2. Open the “Main“ Scene
3. Enable “Domain and Scene Reload” in Edit > Project Settings > Editor
4. Open the “Assets/Screens/Menu.uxml“ file in UI Builder
5. Add a button to the UXML file
6. Enter and Exit Play Mode
7. Observe the UI Builder

Expected result: The UXML file is still loaded
Actual result: The UXML file gets unloaded

Reproducible in: 6000.0.39f1, 6000.0.43f1, 6000.1.0b11, 6000.2.0a7
Not reproducible in: 2022.3.60f1, 6000.0.38f1

Reproduced on: Windows 11 Pro (24H2), MacOS 15.3 (M4)
Not reproduced on: No other environment tested

Notes:
- Only reproducible if both Domain and Scene Reload are enabled Play Mode enabled
- All unsaved changes will be lost upon entering Play Mode
- Sometimes reproduction might require entering and exiting Play Mode twice