Combining a SharePoint query with a BW Message Server query in the PBI Service

Hi, 

I have two queries in my dataset, as follows:

1. SAP BW Message Server ( Source = SapBusinessWarehouse.Cubes("system details", [Implementation="2.0"])). Privacy setting in Permissions in PBI Client is "Organizational".  When query is not combined (or appended) to other queries, it retrieves data in client and PBI Service through a corporate gateway. Corporate Gateway privacy level is "Organizational". Credentials to the on-prem system are provided in the gateway by admin.

2. SharePoint Folder (Source = SharePoint.Files("link to SharePoint Site Root", [ApiVersion = 15])). Privacy setting in Permissions in PBI Client is "Organizational". I am logged onto SharePoint by using my Organizational account in the Client. When query is not combined (or appended) to other queries, it retrieves data in client and PBI Service through what I assume is native MS cloud integration (no gateway configuration needed). Data Source Credentials for SharePoint source is "Organizational", Authentication method is "OAuth2".

When combining or appending above two queries it works in PBI Client. But when published to PBI Service and the BW query (1) is onrolled to the corporate gateway, I get error as follows:

Underlying error code-2147467259

Underlying error messageSharePoint: Request failed: The underlying connection was closed: An unexpected error occurred on a send.

DM_ErrorDetailNameCode_UnderlyingHResult-2147467259

Microsoft.Data.Mashup.ValueError.DataSourceKindSharePoint

Microsoft.Data.Mashup.ValueError.DataSourcePath"SharePoint Site Root" Microsoft.Data.Mashup.ValueError.ReasonDataSource.Error

Cluster URIWABI-NORTH-EUROPE-F-PRIMARY-redirect.analysis.windows.net

Activity ID3020f307-8335-4ad9-b61e-adcc21a0991e

Request IDdbc21882-2018-d44e-b477-a19f736506b2

Time2020-08-28 14:11:24Z

Our Infrastructure Service Provider has not been able to help in the matter and is suggesting yet another gateway to an on-prem file server for insourcing of the flat file instead of using SharePoint. Shouldn't it be possible to combine data from a SharePoint source with any other sources in the PBI Service as it is the PBI Client? What am I doing wrong? Thanks.