windows 10 – How does Windows10 Back up using File History work?

I’m using a mobile hard disk. When I start to back up, multiple “SO” folders are created in the mobile disk. And I noticed most of them have nothing in the “data” subdirectory.

Is this normal? What are these folders used for?

I had just experienced a data loss because of an OneDrive bug (substitute local files with old ones in the cloud). So I ought to be more cautious anyway.-_-.