Error 4xx when accessing SharePoint via Microsoft Graph in specific tenants- Stops working

Question

Since a couple of days, we have realized our Files operations with Sharepoint Sites stop to work with some tenants. We don't have problems accesing OneDrive.

We use Application Permissions in MsGraph, with following Scopes / API Permissions:

• Files.ReadWrite.All (this should be enough)
• Sites.Manage.All
• Sites.ReadWrite.All

We can make a call to get Sharepoint properties:

https://graph.microsoft.com/v1.0/sites/{hostname}:/{server-relative-path}

Sites.ReadWrite.All permission needed for this.

But if i try to list this existing Sharepoint, we get this error in some tenants, with no configuration change on them:

https://graph.microsoft.com/v1.0/sites/{hostname}:/{server-relative-path}/drive/root/children

What configurations in Sharepoint could prevent accesing via MsGraph, when it's possible to access personal OneDrive? Is an error in configuration, domain policy or an error in some Microsoft Tenants?

IS there any channel for paid support from Microsoft for this?