Hybrid Exchange users can't manage Favorite Plans and can't add comments in Microsoft Planner
Content provided by Microsoft
Applies to: Office 365 Planner
Office 365 users may have a Hybrid Exchange configuration where their Exchange mailbox is hosted in an on-premises Exchange environment instead of their in Exchange Online. When they manage Microsoft Planner in this scenario, they experience the following:
They can't view or set Favorite Plans in the Planner Hub and in the left navigation.
They can't view or add comments to a task.
Microsoft is aware of this behavior and is working to improve this experience. There are currently no workarounds available.
Microsoft Planner is enabled by default for users who have eligible Office 365 plans. Current eligible plans include Office 365 Enterprise (E1, E3, E4, and E5), Office 365 Education (E1, E3, E4, and E5), Office 365 Business Essentials, and Office 365 Business Premium.
Microsoft Planner works fully when the user has an Exchange Online mailbox.