Here is a list of things you can do to troubleshoot calendar permissions not syncing in Exchange:

1. Check whether firewall/routers are blocking traffic from Exchange to other endpoints.
2. Make sure the latest versions of Exchange and Outlook are both installed.
3. Check the service account set up by your IT administrator.
4. Reset a user's Outlook client.
5. Check if user's mailbox is in the enabled state.
6. Confirm that the EWS MAPI virtual directory has the correct 'authFlags' set.