How to reproduce:
1. Open the attached project “IN-114113”
2. In the Hierarchy window, select “UIDocument“
3. Lock the Inspector window on “UIDocument”
4. Enter Play mode
5. Observe the result

Alternatively:
1. Open the attached project “IN-114113”
2. Open a second Inspector window
3. In the Hierarchy window, select “UIDocument“
4. Enter Play mode
5. Exit Play mode
6. Observe the result

Expected result: No error messages in the Console window
Actual result: Several error messages in the Console window

Reproducible with: 6000.2.1f1, 6000.2.3f1, 6000.3.0a5(f9a1fab5607a), 6000.3.0b1
Not reproducible with: 6000.0.57f1, 6000.2.0f1(eed1c594c913), 6000.3.0a4

Reproduced on: macOS 15.6 (M1)
Not reproduced on: No other environment tested

Note: Error Message: MissingReferenceException: The object of type 'UnityEngine.UIElements.UIDocument' has been destroyed but you are still trying to access it.