Steps to reproduce:
1. Open the attached “IN-153567_PreviewSceneStageBug.zip” project
2. Open Bug -> Open Preview Scene
3. Start dragging the "Preview" scene in the Hierarchy window
4. Observe the Console
Actual result: InvalidOperationException or ArgumentNullException error is thrown in the console (depending on the version)
Expected result: No errors are thrown
Reproducible with: 6000.3.0a2, 6000.3.24f1, 6000.6.0a1
Not reproducible with: 6000.6.1f1, 6000.7.0a6
Fixed in: 6000.6.0a2
Could not test with: 6000.0.84f1 (Hierarchy V2 is not available)
Reproducible on: macOS Sequoia 15.7.9 (M1 Max)
Not reproducible on: No other environments tested
Note: In Unity 6.3 the New Hierarchy window is found under Preferences → General and not Project Settings