If the problem doesn’t occur after you restart Outlook, one of the add-ins is likely the cause of the problem. Restore the add-ins one at a time until the problem does occur to determine which add-in is causing the problem. Although add-ins can enhance your user experience, they can occasionally interfere or conflict with Outlook. Try to start Outlook without any add-ins running.

In some specific cases, we observed that the problem no longer stayed after deleting the Outlook App Data folder. Thus, you can try deleting the Outlook App Data folder and check whether Outlook functions in your case