Hi @Cliff Freed ,
Welcome to our fourm!
What's the type of your account? (IMAP/POP/Exchange)
And what's the version of your Outlook? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.
In addition, have you done any specific operations before the issue occurred?
Considering that it may be caused by the damage of the profile/data file in the Outlook client, it is suggested that you could try to create a new profile(Control Panel>Mail>Show Profiles>add) and add the account for testing to check if there are some differences.
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.