With Exchange hybrid mode , when your mailbox is still onprem and you are using outlook for mobile, you may have issues with duplicate mail items or calendar items. Sometimes items that were deleted are show on outlook for mobile but not on OWA or outlook for desktop.
The problem can get worst if you make a bulk of meeting deletion or creation Via PowerShell or over programing method.
To avoid such issues, Microsoft recommend using the Outlook desktop client or OWA to perform the changes directly in the mailbox calendar.
The user will need to proceed as follows for bulk deletion:
1 Open Outlook for Windows and switch to Calendar view
2 Select View – Change View to “List”
3 Sort items by date and use the Ctrl+C+down key to select items and then press Delete.
Mailbox Cloud-Cache
With Exchange hybrid mode , when your mailbox is still On- prem and you are using outlook for mobile. your outlook client on mobile connect to mailbox cloud-cache (an object on cloud that sync to your onprem mailbox ) and not to exchange online or Exchange Onprem. you cant see the content in the cloud-cache or access the data with powershell or any method beside outlook for mobile.
In this Scenario cloud-cache contain all your Calendar Items and Only 4 Weeks of Mails.
Reset the Cache
If you happen to encounter a situation where the old deleted meetings are still showing in the calendar of an on-prem user mailbox in the Outlook mobile app, you can follow the steps below:
Please try cmdlet no.1) first in order to reset the Cloud-Cache:
1) # Partial delete that will maintain the log-in state (The access Token is not revoked):
Set-User $IdOrEmailAddress -DesiredWorkloads CCStrategicReserve
2) # Partial delete that will require logging back-in (The access Token is revoked):
Set-User $IdOrEmailAddress -DesiredWorkloads Substrate
Please note that it can take at least 7-8 hours after running the cmdlets above for the partial delete to complete.
To check the status of the operation, you can run the cmdlets below :
Get-User $IdOrEmailAddress | fl Desired
If “DesiredWorkloads” is null, the partial delete is complete.
If you run the first cmdlet and then check the status after 24h and “DesiredWorkloads” does not return “null”, you can try to run the second command and wait approx. 8 hours.
If that did not help either, you should open a support request on Microsoft so that they can look into it on backend.
SHMUEL H.