Hi @MeredithCubero, Yvette M ,
Thanks for your reply!
In order to further confirm if the issue is related to Outlook client, it's suggested that you could log in to web mail and check if the categories persists.
If there's no categories on web mail, i'm afraid that the categories cannot be recovered.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.