"NullReferenceException" is thrown and Mesh LOD foldout is empty when maximizing Inspector with "Mesh LOD" property

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Drag the attached "model.fbx" to the Project window
3. Select the "model.fbx" asset
4. In the Inspector, enable the "Generate Mesh LODs" property
5. Click Apply
6. Drag the asset into the Hierarchy or Scene
7. Maximise its Inspector by double-clicking on the Inspector tab

Actual results: "NullReferenceException: Object reference not set to an instance of an object" is thrown and Mesh LOD foldout is empty

Expected results: No errors and the foldout content is visible

Reproducible with versions: 6000.4.0a1, 6000.4.0b4, 6000.5.0a4

Not reproducible with versions: 6000.0.65f1, 6000.3.0a6, 6000.3.4f1

Tested on (OS): Windows 11, macOS Tahoe 26.1 (M1)