I've been in contact with Microsoft support now and they stated:
"The issue you are experiencing is due to an unexpected defect surfaced on our end which caused service outage in Power BI SERVICE System. We already posted in https://powerbi.microsoft.com/en-us/support/ for users awareness. Our team got fixed this issue [...] 3AM PDT [=12PM CEST, September 8th 2020] and then removed comms from the portal. This is specific to Europe region.
Impact : users may experience intermittent delays while accessing the power BI service. [...] Hope you will not see this behavior again".