Images not showing in Catalog folders in LrC - Windows 10 system

That would typically happen when the user has removed all the images that were cataloged in those folders. The images that you see in File Explorer could be either images that were in the catalog and have been removed from LrC, or images that have never been imported into LrC, or a mixture of both. If they are previously cataloged images that have been removed from the catalog, only you would be able to figure out how that may have been done, but if it was unintentional then you need to think about trying to recover the situation by looking at your catalog backups. If that's not possible, you could right-click on each folder and select "Synchronize Folder" which would import the images, but you would have lost all previous work done in LrC unless you had saved metadata to XMP.