Personally I haven't had much luck with the USB-SD Creator tool in Ubuntu, although this was mostly in 16.04. I haven't even tried lately in 20.04. After several failures I switched over to Rufus in Windows... That tool got the job done in 1 go. C'est la vie.
Also the initial developer of the USB-SD tool is no longer available for updates. But, any disk-image writing tool can be used the LibreELEC disk image. Even 'dd' in Linux with the correct parameters.