I have a shared mailbox in Office 365 with a shared calendar. Users are granted Publishing Author permission to the calendar folder using Exchange Online PowerShell and these permissions are confirmed using Outlook during troubleshooting.
The problem is that a new user we're setting up can only see the Default permissions, despite being granted the same permissions as everyone else. The user hasn't signed in yet so I'm able to log in to OWA using their account and it shows only the free/busy status for this calendar. If I update the Default permission to show full details, their OWA calendar view updates immediately to reflect the change. But changing their explicit permissions (Publishing Author, Editor, Publishing Editor) makes no difference at all. SharingPermissionFlags is $null for all users with access rights (including Default). So far no other users have reported any problems viewing or accessing the calendar, so this appears isolated to this one new user.
Based on my testing, I don't think this is an issue with folder permissions differing from calendar permissions, though it certainly looks like it. The behavior is exactly as though OWA/Exchange Online doesn't even recognize the user has explicit permissions at all. I conclude this because changing the permissions on the Default user affect this user's view.
In the below (sanitized) screenshot, the first user after Anonymous is unable to view any calendar item details, they can only see availability. All other users have access as expected. Once I set the Default permission to "Reviewer", they can see all details and interact with the calendar as expected. These are Office 365 mailboxes and both the target calendar and the user have Office 365 E1 licenses.
Something else that is extra weird is that when I set the Default permission to "AvailabilityOnly", this user cannot view or interact with the calendar beyond free/busy status. However, when I set the Default permission to Reviewer, this user can fully interact with the calendar with the explicit PublishingAuthor permission we've granted. If I set the Default permission back to AvailabilityOnly, the user again cannot view or interact with the calendar beyond seeing free/busy status.
Has anyone else experienced this and been able to resolve it?