Hi WynHopkins,
Based on your description, please try the steps below to check whether the issue persists:
1.Please ensure you have install the latest updates.
2.Follow this article to repair Excel 2016: Repair an Office application.
3.If repairing is not working, please use the Easy Fix tool in this article to completely uninstall Office and then reinstall Office: Uninstall Office 2016, Office 2013, or Office 365 from a PC.
Regards,
Fraser