Refreshes fail when using combined models with PBI Datasets

Hi,

I'm working on a report where I combine several PowerBI datasets (via Direct Query) and additional imported tables. This all works fine in Power BI Dekstop. I can refresh the data for the imported tables without any issue. But as soon as I publish the dataset and try to refresh the imported tables via Power BI Service, it flat out fails. It keeps coming back with vague errors about wrong credentials. I litterally tried everything, (i.e. reset the credentials, privacy levels, etc.) but nothing works and I'm 100% sure the credentials are correct.

Does anyone have an answer to this?

Thanks.

Regards,

Maarten