Commented Unassigned: SSH.NET Upload Multiple files asynchronously throws an exception. [2408]

I am creating an application that will

1. process a CSV file,
2. create JObject for each record in CSV file, and finally
3. upload all these files to SFTP server

After looking around for a free library for the 3rd point, I decided to use SSH.NET.

I have created the following class to perform the upload operation asynchronously.

public class JsonFtpClient : IJsonFtpClient
{
private string _sfptServerIp, _sfptUsername, _sfptPassword;

public JsonFtpClient(string sfptServerIp, string sfptUsername, string sfptPassword)
{
_sfptServerIp = sfptServerIp;
_sfptUsername = sfptUsername;
_sfptPassword = sfptPassword;
}

public Task<string> UploadDocumentAsync(string sourceFilePath, string destinationFilePath)
{
return Task.Run(() =>
{
using (var client = new SftpClient(_sfptServerIp, _sfptUsername, _sfptPassword))
{
//ALL ERRORS ARE THROWN WHEN EXECUTING THIS LINE
client.Connect();

using (Stream stream = File.OpenRead(sourceFilePath))
{
client.UploadFile(stream, destinationFilePath);
}

client.Disconnect();
}

return (destinationFilePath);
});
}
}

The UploadDocumentAsync method returns a TPL Task so that I can call it to upload multiple files asynchronously.

I call this UploadDocumentAsync method from the following method which is in a different class:

private async Task<int> ProcessJsonObjects(List<JObject> jsons)
{
var uploadTasks = new List<Task>();
foreach (JObject jsonObj in jsons)
{
var fileName = string.Format("{0}{1}", Guid.NewGuid(), ".txt");

//save the file to a temp location
FileHelper.SaveTextIntoFile(AppSettings.ProcessedJsonMainFolder, fileName, jsonObj.ToString());

//call the FTP client class and store the Task in a collection
var uploadTask = _ftpClient.UploadDocumentAsync(
Path.Combine(AppSettings.ProcessedJsonMainFolder, fileName),
string.Format("/Files/{0}", fileName));

uploadTasks.Add(uploadTask);
}

//wait for all files to be uploaded
await Task.WhenAll(uploadTasks);

return jsons.Count();
}

Although the CSV file results in thousands of JSON records, but I want to upload these in batches of at least 50. This ProcessJsonObjects always receives a list of 50 JObjects at a time which I want to upload asynchronously to the SFTP server. But I receive the following error on client.Connect(); line of the UploadDocumentAsync method:

Session operation has timed out

Decreasing the batch size to 20 results in the following error:

Client not connected.

But this also uploads 3 files to the SFTP server as well, but not all the 20.

What am I doing wrong? Your help is much appreciated.
Comments: ** Comment from web user: drieseng **

Please upload a full VS project that shows this issue.
Thanks!