Can't view files in Sharepoint but can see them in File Explorer

Many thanks for your reply Adam. We have set-up lots of sites and copied data into them in exactly the same way and this is the only one we have an issue with. But following your advice, I have rechecked and what is happening is, the SharePoint document library isn't showing any files, when you take the 'view in file explorer' option it is actually opening another view of SharePoint showing a library tab at the top of the page. When you click on the library tab and take the view in explorer option it then opens the file explorer window. Any idea what is happening please, this is going to be confusing for the site users? Thanks.