Request denied adding app role through AD GraphClient

We have since this week an issue applying app roles through the latest AD Graphclient (2.1.0).

We authenticate to ActiveDirectoryClient as an application (registered under the AAD) using ClientId, ClientSecretKey etc.

Also the permissions are correctly set for the application, but since this week we get an error back.

odata.error":{"code":"Authorization_RequestDenied","message":{"lang":"en","value":"Insufficient privileges to complete the operation.}}

Strange thing is, of course, that it worked like a charm before.

Does anyone have an idea what changed since this week? Did we miss an announcement that explains this sudden non-functioning?