Geo: Failures downloading import/export files

I applied https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6567 to one of the GPRD nodes, and then I tried running the steps in https://gitlab.com/gitlab-com/migration/blob/master/runbooks/geo/attachment-sync-failures-and-unsynced.md#sync-unsynced-uploads. I saw these failures:

Failed: #<Geo::FileRegistry id: 14250257, file_type: "import_export", file_id: 4550946, bytes: 0, sha256: nil, created_at: "2018-07-21 06:18:47", success: false, retry_count: 1, retry_at: "2018-07-21 06:19:15", missing_on_primary: false>
Failed: #<Geo::FileRegistry id: 14250258, file_type: "import_export", file_id: 4565970, bytes: 0, sha256: nil, created_at: "2018-07-21 06:18:51", success: false, retry_count: 1, retry_at: "2018-07-21 06:19:29", missing_on_primary: false>
Failed: #<Geo::FileRegistry id: 14250259, file_type: "import_export", file_id: 4566001, bytes: 0, sha256: nil, created_at: "2018-07-21 06:18:56", success: false, retry_count: 1, retry_at: "2018-07-21 06:19:34", missing_on_primary: false>
Failed: #<Geo::FileRegistry id: 14250260, file_type: "import_export", file_id: 4566004, bytes: 0, sha256: nil, created_at: "2018-07-21 06:19:02", success: false, retry_count: 1, retry_at: "2018-07-21 06:19:32", missing_on_primary: false>
Failed: #<Geo::FileRegistry id: 14250261, file_type: "import_export", file_id: 4566006, bytes: 0, sha256: nil, created_at: "2018-07-21 06:19:07", success: false, retry_count: 1, retry_at: "2018-07-21 06:20:19", missing_on_primary: false>
Failed: #<Geo::FileRegistry id: 14250262, file_type: "import_export", file_id: 4566050, bytes: 0, sha256: nil, created_at: "2018-07-21 06:19:13", success: false, retry_count: 1, retry_at: "2018-07-21 06:20:23", missing_on_primary: false>

/cc: @mkozono, @jameslopez