Comment 1 for bug 1764534

Happened here also:

Traceback (innermost last):
  File "/usr/bin/duplicity", line 1562, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1548, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1400, in main
    do_backup(action)
  File "/usr/bin/duplicity", line 1426, in do_backup
    action).set_values()
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 710, in set_values
    self.get_backup_chains(partials + backend_filename_list)
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 836, in get_backup_chains
    add_to_sets(f)
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 824, in add_to_sets
    if set.add_filename(filename):
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 105, in add_filename
    (self.volume_name_dict, filename)
 AssertionError: ({1: 'duplicity-full.20180512T001010Z.vol1.difftar.gpg', 2: 'duplicity-full.20180512T001010Z.vol2.difftar.gpg', 3: 'duplicity-full.20180512T001010Z.vol3.difftar.gpg', 10: 'duplicity-full.20180512T001010Z.vol10.difftar.gz', 11: 'duplicity-full.20180512T001010Z.vol11.difftar.gz', 12: 'duplicity-full.20180512T001010Z.vol12.difftar.gz', 13: 'duplicity-full.20180512T001010Z.vol13.difftar.gz', 14: 'duplicity-full.20180512T001010Z.vol14.difftar.gz', 15: 'duplicity-full.20180512T001010Z.vol15.difftar.gz', 16: 'duplicity-full.20180512T001010Z.vol16.difftar.gz', 17: 'duplicity-full.20180512T001010Z.vol17.difftar.gz', 18: 'duplicity-full.20180512T001010Z.vol18.difftar.gz', 19: 'duplicity-full.20180512T001010Z.vol19.difftar.gz', 20: 'duplicity-full.20180512T001010Z.vol20.difftar.gz', 21: 'duplicity-full.20180512T001010Z.vol21.difftar.gz', 22: 'duplicity-full.20180512T001010Z.vol22.difftar.gz', 23: 'duplicity-full.20180512T001010Z.vol23.difftar.gz', 24: 'duplicity-full.20180512T001010Z.vol24.difftar.gz', 25: 'duplicity-full.20180512T001010Z.vol25.difftar.gz', 26: 'duplicity-full.20180512T001010Z.vol26.difftar.gz', 27: 'duplicity-full.20180512T001010Z.vol27.difftar.gz', 28: 'duplicity-full.20180512T001010Z.vol28.difftar.gz', 29: 'duplicity-full.20180512T001010Z.vol29.difftar.gz'}, 'duplicity-full.20180512T001010Z.vol3.difftar.gz')