Hi @MarioSiebeck-5459,
Hope you are doing well,
This seems to be a tenant specific issue, to address your queries on the same we would recommend you to raise a support case with Microsoft support team , Respective Support Engineer will be able to assist you on the same . You can raise support ticket using below links
http://aad.portal.azure.com/
https://admin.microsoft.com/#/support/requests.
Hope this helps.
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