How to reproduce:
1. Create and open a new project
2. Create a new UXML (UI Document) asset
3. Open the newly created file and add a Visual Element
4. Save and close the UI Builder
5. Create another UXML asset and open in UI Builder
6. Add a Multi-Column List View to the Hierarchy
7. In the Inspector, Attributes section, expand both Columns properties
8. Add a new column to the list
9. In the Cell Template field assign the first created UXML
10. Click in the Hierarchy to deselect the visual element
11. Save and close the UI Builder
12. Reopen the first created UXML
13. Make any change (remove/add a visual element) save and close the UI Builder
14. Reopen the second UXML
15. Observe the Console and UI Builder Inspector

Actual result: An “ArgumentException” error is thrown in the Console and Cell Template field is reset back to None
Expected result: No errors are thrown and Cell Template remains populated

Reproducible with: 6000.0.0b15, 6000.0.71f1, 6000.3.12f1, 6000.4.0a1
Not reproducible with: 6000.4.0a2, 6000.4.0f1, 6000.5.0b1, 6000.6.0a1
Fixed in: 6000.4.0a2

Reproducible on: macOS 26.3 (M1 Pro)
Not reproducible on: No other environment tested

Notes:
- Likely other scenarios exist to reproduce the issue, the proposed one yielded most consistent reproduction
- Error thrown: “ArgumentException: Object of type 'UnityEngine.Object' cannot be converted to type 'UnityEngine.UIElements.VisualTreeAsset'“
- The issue is less consistent the older the Editor version