SSHException Channel was closed intermittent behavior

We are connecting to a client SFTP and prior to this week had nothing but successful transactions.
We are now experiencing intermittent exceptions. We are calling this functionality from an Azure function, and the files are streamed from Azure storage, but i don't believe that has any impact on the issue.
I have tried both synchronous and asynchronous methods and had success locally, and on majority of live test cases, but when it fails, I don't have an idea of what the problem may be. Any thoughts would be much appreciated.

My code is below:

sftpClient.Connect();
var uploadPath = $"{sftpFolder}/{fileName}";
sftpClient.UploadFile(stream, uploadPath);
sftpClient.Disconnect();

Alternatively, I tried instead:

sftpClient.Connect();
var uploadPath = $"{sftpFolder}/{fileName}";
var returnVal = sftpClient.BeginUploadFile(stream, uploadPath, new AsyncCallback(x => FileTransferred(x, log, fileName, uploadPath)));

Beginnen Sie mit den gemeldeten Connect(), UploadFile() und BeginUploadFile()-Aufrufen und vergleichen Sie den intermittierenden Fehler in der Azure Function mit erfolgreichen lokalen Läufen. Erfassen Sie den vollständigen Kontext der SSHException sowie die Verbindungs- oder Übertragungsbedingungen; abgeschlossen ist die Aufgabe, wenn eine reproduzierbare Ursache identifiziert und eine Behebung der intermittierenden Kanalschließung dokumentiert oder validiert wurde.