..it's quite common to have problems with viewing actual files within the folders. Windows Backup isn't an ideal way of actually making copies from one computer to another. Instead, if you're trying to backup the entire computer, make a disk image using various types of disk image software. Windows 10 still has an option to create a disk image in the Control Panel-Backup and Restore (Windows 7) or there are other types of disk image software available.

On the other hand, if your having problems doing a simply copy and paste of folders which contain files, then that's a different issue. If that's the problem, then try using a different USB drive. You didn't say whether the USB device is an external hard drive, which are frequently known as unreliable and could be the root of the problem if its failing, or a USB flash drive. Either way, try a different one.

Hope this helps.