NB xbFootnoteTag is now deprecated and replaced by xbRefs.

If you have xbFootnoteTag installed and wish to preserve your existing references ({ xbref...} shortcodes) then please update to this latest version (1.2.0) and check the Content plugin new option is NOT to delete existing references on uninstall, then uninstall and install a fresh xbRefs Plugins package and enable the new plugin.

If you don't mind loosing any existing shortcodes then uninstall xbFootnote tag and install xbRefs-Plugins package in its place.

See xbRefs article and documentation for more details