Exchange Online Calendar Permissions

[Sahin Boluk]

Hi, after migrating from Exchange hosted to MS 365, we have noticed that a few users calendar permissions for "My Organization" changes to None.  We run a script to update/change the permissions to AvailabilityOnly, but overnight it changes back to None.  This happens to almost half of our users and not the other half.  I was not able to figure out why, how or where to look as to why this happens, any suggestions 

[#2]

The Default value in O365 is "AvailabilityOnly", you most likely have some background process updating this. Check the admin audit logs in Exchange/Unified Audit Log in the SCC.

[#3]

@Vasil Michev , thanks but noting in the audit logs for one of the users and I just checked and the permissions were changed back to None.  Audit logs shows nothing for the user and I'm searching for all activities. 

[#4]

What I have also just noticed a few days ago is if I try to add a userA to UserB calendar as Reviewer, get the error below.

Also, I give any other permissions EXCEPT reviewer, very odd.  When I do it manually, it also last for what seems like 24 hours.

No idea what to do nect.

Your request can't be completed. You don't have permission to share this calendar.
+ CategoryInfo : NotSpecified: (:) [Add-MailboxFolderPermission], InvalidRequestException
+ FullyQualifiedErrorId : [Server=BL0PR22MB2402,RequestId=5bfe7ff7-d9f5-478b-ace9-c9a4722ee9eb,TimeStamp=1/16/2021 7:40:18 PM] [FailureCategory=Cmdlet-InvalidRequestException] 9949D389,Microsoft.Exchange.Management.StoreTasks.AddMailboxFolderPermission
+ PSComputerName : outlook.office365.com