Steps to repro:
1. Open the attached project and load the 'Night' scene;
2. Drag and drop 'geometry' scene from the Project folder to the Hierarchy window;
3. Make sure that the 'Night' scene is set as the main (master) scene in the Hierarchy;
4. In the Lighting setting window (Window>Rendering>Lighting) click Generate Lighting button and wait until the scene's lighting is baked;
5. In the Hierarchy right click on the Night scene and select "Unload Scene";
6. Drag and drop 'Day' scene from the Project folder to the Hierarchy window;
7. In the Hierarchy, double-click on the Day scene to make it the main (master) scene;
8. In the Lighting window open the Baked Lightmap tab;
9. Expand the Lighting Data Asset dropdown list and select "LightingData-1" file;
10. In the Lighting Data Asset dropdown list select "LightingData-1" belonging to the "Night" scene.

Expected result:
The lighting data asset is replaced for the active scene without errors.

Actual result:
Errors:
"Assertion failed on expression: 'manager != NULL'
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)"
are shown in the Console.

Regression introduced in Version 2021.2.0a1.

Notes:
- Reproducible in Version 2021.2.0a7, 2021.2.0a6, 2021.2.0a4, 2021.2.0a3, 2021.2.0a2, 2021.2.0a1;
- Not reproducible in Version 2021.1.0b9, 2020.2.7f1;
- Reproducible on OSX and Windows;
- If the Editor doesn't allow to manually assign the lighting data asset file in the dropdown, try dragging the asset file to the Lighting Data Asset field of the Lighting window, this should also trigger the bug.