The expiration policy will treat a group is active based on three activities only: SharePoint, Outlook, Teams. How about those activities in Power BI, Planner, Project and Stream? A Office 365 Group can be used without Teams enabled and used for those 4 services only. The group owner will receive the expiration notification email (the email is not mentioning these services at all) and may just delete the group (even it is actively in used in that 4 services). Please include the expiration policy for those activity used in that 4 services.