It looks like you manually unzipped volume 632, the last volume in the listing. This causes problems since it leaves the volume as a difftar, not a difftar.gz.
Go into your backup and
$ gzip duplicity-full.20190805T173846Z.vol632.difftar
and that will allow duplicity to finish.
In the future, don't play with the backup files.
It looks like you manually unzipped volume 632, the last volume in the listing. This causes problems since it leaves the volume as a difftar, not a difftar.gz.
Go into your backup and
$ gzip duplicity- full.20190805T1 73846Z. vol632. difftar
and that will allow duplicity to finish.
In the future, don't play with the backup files.