Comment 6 for bug 1974138

Disabling and Enabling the Sync for a given bucket from the primary site does the re-sync trick:

$ sudo radosgw-admin bucket sync disable --bucket backup-archive
$ sudo radosgw-admin bucket sync enable --bucket backup-archive

$ sudo radosgw-admin bucket sync status --bucket backup-archive
          realm 0b1d60c6-5be8-470a-9d58-4e6a1215848b (hrizn.cloud)
      zonegroup 1be243bd-7041-4343-8202-3e47b2f28c76 (int.hrizn.cloud)
           zone 1d914e95-58bc-411c-a4fa-306dd2191344 (s3-az1)
         bucket :backup-archive[1d914e95-58bc-411c-a4fa-306dd2191344.22094132.2])

    source zone d46023eb-6350-4536-9440-7ea24ae270fa (s3-az2)
  source bucket :backup-archive[1d914e95-58bc-411c-a4fa-306dd2191344.22094132.2])
                full sync: 0/11 shards
                incremental sync: 11/11 shards
                bucket is behind on 1 shards
                behind shards: [8]