Third attempt failed with the following error, same as the first:

Last full backup date: Tue Aug 14 04:23:11 2018
Invalid data - SHA1 hash mismatch for file:
 duplicity-full.20180814T042311Z.vol11.difftar.gpg
 Calculated hash: a257e115e232bc9780bd25314edfccc4ee337981
 Manifest hash: 4e474e1e6038c3c7f1c516d615c79a729aaa83f4

Think I have a clock problem.  Fixed the time zone and the host clock sync, trying again.