A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Ashley,
We suggest you confirm if you enable the SharePoint Server Publishing Infrastructure feature on the site collection level: Enable publishing features
For detailed information, refer to this article: Enable managed navigation for a site in SharePoint
Also, we'd like to confirm the following information for troubleshooting:
1.Your detailed steps before getting the error message.
2.Have you checked the result in different browsers/browser private mode?
3.Does the error happen in other SharePoint sites?
Regards,
Tina