May 2021 Gateway Error: SharePoint: Request failed: The underlying connection was closed.

Hi,

SharePoint: Request failed: The underlying connection was closed: An unexpected error occurred on a send:

The following replicates the above error we are seeing both with SharePoint List and Excel Online:

The data is too small to be an optimisation issue.

I have set up a very simple pbix and connected it to a SharePoint List and to a SQL On Premises table.

SharePoint has 32 rows , SQL has 330 rows. 

I publish this pbix to our Premium Service and select our Gateway for the SQL and oAuth2 for SharePoint.

Scheculed Refrsh works - All Good.

If I take the same file and Merge SharePoint and SQL, everthing works as expected and refreshes in the desktop.

I publish this pbix to our Premium Service and again select the Gateway for SQL and oAuth2 for SharePoint. I also ensure Privacy Levels are the same : ( Both Organizational or Both Private or Both Public)

Scheduled Refresh FAILS each time.

SharePoint: Request failed: The underlying connection was closed: An unexpected error occurred on a send

If I wrap the SharePoint List with a Dataflow and update the merge to use SQL and the Dataflow instead, the Scheduled Refresh works.

All this happens for Excel Online aswell.