SPOWebAppServicePrincipal stopped working

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

SharePoint CSOM

Developer environment

Windows

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

CSOM Version: 16.1.25611.12000 (older versions show the same behaviour)

Describe the bug / error

The following C# code using CSOM did work for several years. Now it suddenly throws an 'unknown error' during runtime:

using (ClientContext adminContext = this.authenticationManager.GetContext(this.spAdminUrl))
{
    var servicePrincipal = new SPOWebAppServicePrincipal(adminContext);
    var permissionGrants = servicePrincipal.PermissionGrants;
    var permissionRequests = servicePrincipal.PermissionRequests;
    adminContext.Load(permissionRequests);
    adminContext.Load(permissionGrants);
    adminContext.ExecuteQueryRetry();
}

Steps to reproduce

1. Get an access Token for an admin user (Global Admin or SharePoint Admin)
2. Initialize AuthenticationManager with that access token
3. Execute the code in the description above

Expected behavior

The execution should return pending requests and already approved grants.
But it only throws an 'unknown error':
Microsoft.SharePoint.Client.ServerException: Unbekannter Fehler. at Microsoft.SharePoint.Client.ClientRequest.ProcessResponseStream(Stream responseStream) at Microsoft.SharePoint.Client.ClientRequest.ProcessResponse() at Microsoft.SharePoint.Client.ClientRequest.<ExecuteQueryToServerAsync>d__53.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.SharePoint.Client.ClientRequest.<ExecuteQueryAsync>d__39.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.SharePoint.Client.ClientRuntimeContext.<ExecuteQueryAsync>d__65.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.SharePoint.Client.ClientContext.<ExecuteQueryAsync>d__28.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at Microsoft.SharePoint.Client.ClientContextExtensions.<ExecuteQueryImplementation>d__6.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.SharePoint.Client.ClientContextExtensions.ExecuteQueryRetry(ClientRuntimeContext clientContext, Int32 retryCount, String userAgent)
Maybe this is related to the changes made for issue #9962