Gateway Mashup Error When Combining File from SharePoint with a File on Network Folder

[newpbiuser01]

Hello,

I have a report that was connected to an Excel file on a SharePoint site. The file refreshes just fine on a regular basis. I now have an additional file (csv) that I appeneded to this file - which is stored on a network folder. I append these two and refresh the data in Desktop without any issues. When I try to do that in Power BI Service - I get the Pipeline Gateway Mashup Data Access Error.

When I remove the newly added csv file, the report refreshes without any issues in Service. What am I doing wrong? The table that's throwing an error here is the appended table with both the files. I have not made any changes to the SharePoint file or the query (the file names etc are all the same). I've checked the sensitivity labels and it's set to Organizational for both. 

Why is the refresh failing in Power BI Service and not in Power BI Desktop?

I'd really appreciate any help!

[lbendlin]

I got bad news for you.  When you are attempting to merge/append a cloud data source with an on-premise data source then you need to create a gateway connection for the cloud data source (yes, crazy, I know). It gets even worse. Once you connect to the cloud source via gateway you will never ever be able to revert, even if you subsequently remove the on-prem data source.

Put your CSV file on the same sharepoint.