Whenever I schedule a sync or copy using the backup functionality (to USB or between internal folders) the destination folder ends up not being the the one I picked up, but some folders within a new folder that has the name of the job I’ve created.
When you set up the USB backup, do you enable the option to auto start when you connect a USB drive ? I believe that when you enable this option, you are able to backup to the same destination, also there is a drop down that has the incremental option, you can also try this.