Yesterday a colleague of mine had problem to setup a schedule refresh at a Power BI file on a Power BI Report Server. The refresh fails every time with an error message that the credentials are missing for the data source. But the credentials are setup for the data source. It seems that we entered in an error from the October release (https://community.powerbi.com/t5/Report-Server/Power-BI-Report-Server-October-2020-update-has-been-released/td-p/1503433). But the error was fixed, and we had installed the updated release.
The fix was easy, because when you create connections to an earlier data source, but with another notation, you get two different connections:

For the Power BI service this is not an issue, but the Report Server thinks there two connections, but you will only see one of them at data source wizard. So, when you harmonize the notations and publish the report again to the report server, the scheduled refresh works correctly.