makeEwsRequestAsync randomly generates error - outlook

Question

I'm using Office JavaScript API to edit and save emails through an Add-in.
To get all attachments of an email, I use makeEwsRequestAsync. Most of the time the method is successful but sometimes it returns this error:
Failed to make a request via HttpWebRequest.
Exception: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host.
{
"value": null,
"status": "failed",
"error": {
"name": "GenericResponseError",
"message": "Failed to make a request via `HttpWebRequest`. Exception: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host.",
"code ": 9020
}
}
I'm working with Outlook 2016 Online (Office 365 ProPlus Version 1711) and I got the error on Windows 10 machine using both Chrome and Edge browsers.
EDIT:
Here is the full scenario:
Create new email
Hit send button
Add-in will intercept send event
Add-in saves email under draft using Office.context.mailbox.item.saveAsync that will return itemId
Once itemId is returned, try to load email headers and attachments (in parallel) by calling two makeEwsRequestAsync methods (using itemId with properly formated XML)
I can only think about 3 issues:
Is it possible that saveAsync returns an itemId that does not exist yet?
But in this case, I'm expecting a different error message.
Does calling 2 makeEwsRequestAsync simultaneously is problematic?
I don't think so. JavaScript is single threaded and the 2 methods are never called at the same time.
Is there a session timeout to communicate with EWS API?
Also, The error happens in different mailboxes and there is no other prior or post error.