If you’re having issues with missing or disappeared calendar invitations in Outlook, here are some things to try:

1. Check your Junk mail folder in Outlook.
2. Check your Clutter mailbox in Outlook.
3. Check other email accounts you might have connected to Outlook.
4. Check to make sure your add-ins are up to date.
5. Verify that Outlook isn’t running in Cached Exchange Mode.
6. Check the calendar invitee to ensure that the invitation process was successful.
7. Make sure filters are turned off.