Several probable causes of the Outlook calendar appointments not showing issues include the following. Assume you accidentally erased an appointment on your phone. In such an instance, you'll see that appointments have vanished from the system outlook application as a result of synchronizing. Outlook automatically deletes previous appointments. Outlook optimizes its data files on a regular basis and deletes obsolete appointments. Additionally, if the auto-archive option is activated, Outlook Calendar Appointments are missing. Outlook archives appointments when they become obsolete or after a specified time period.