Catch exceptions when viewing a single batch and simply return readyForDownload=false if readyForDownload is false and the download fails again.

BulkPrintingAPI/Controllers/BatchesController.cs

 
             if (!batch.ReadyForDownload)
             {
-                await Utils.DownloadVouchersAsync(_sftpOptions, _context, _logger, batch);
+                try
+                {
+                    await Utils.DownloadVouchersAsync(_sftpOptions, _context, _logger, batch);
+                }
+                catch (Exception e)
+                {
+                    _logger.LogError(string.Format(
+                        "Failed to download vouchers for {0} batchId={1}: {2}",
+                        credentials.ToString(), batch.Id, e.Message));
+                }
             }
 
             return Ok(batch);