Thumbnails do not display shadows after opening and saving the asset

Shadows in an asset's thumbnail disappear after opening and saving the asset, whether changes are made or not. 

Tested: 4.24.3 CL#11590370, 4.25P6 CL#12493028, 4.26 CL#12767035

1. Create a project with Raytracing enabled and using DirectX12
2. Open any static mesh asset
3. Do not make changes, only press save and close the asset editor window
4. Observe the thumbnail after saving the asset.

Result: The existing shadow in the asset's thumbnail will disappear.

Expected: The shadow to remain after saving and closing the asset.