PBIRS rest api, data to Power BI report, authentication

Did not need to wait for the server to reboot. Found the problem. 

After some deeper digging I found reports that were "shut out" of admin persons, i.e. the BUILTIN\Administrators had been removed from the security page for the reports. After adding BUILTIN\Administrators with Content Manager rights where it was missing, the datasource report is now refreshing fine. 

Here's a query that helped me out:

with a as (
select PolicyID
from [ReportServer].[dbo].[PolicyUserRole] (nolock)
where UserID = '<GUID>' --get the ID from table 'Users'
)
select * 
from Catalog c (nolock)
where not exists (
	select 1 
	from a 
	where a.PolicyID = c.PolicyID
)
and path not like '%Users Folders%'

Have a nice day!