When you create a modern group in Microsoft Outlook Web App (OWA) and then add the group calendar in Microsoft Outlook 2013, group members' calendars are displayed instead of the group calendar in Outlook 2013.
This behavior is by design. Outlook 2013 does not support the modern group calendar. You can use this feature only in Outlook 2016 and Outlook Web App.
Article ID: 3088174 - Last Review: 23 Sep 2015 - Revision: 1