PowerBI report server scale-out with NLB - bad request when open or upload PowerBI Report

[JulesE]

I have setup 2 PowerBI Report Servers in an scale-out deployment with an NLB (https://docs.microsoft.com/en-us/sql/reporting-services/report-server/configure-a-report-server-on-a...)

When opening the load balancer URL i can login, create folders, assign permissions. But when i try to open a powerbi report or try to upload a report an error occured.

In the RSPortal.log i find the following error:

2019-09-25 17:52:47.1644|ERROR|41|The remote server returned an error: (400) Bad Request.| RequestID = s_c1a68a9f-38c0-4e89-ab27-045f4ca39fbe

I'm using Microsoft Power BI Report Server - May 2019.

When creating a report with PowerBI Desktop for Reporting Services (also May 2019 version) and try to save that report on the report server the following error message appears:

Would be glad if anyone can help.

Thanks,

JE