Have a page called 404. To add a custom 404 page as per the documentation here: https://our.umbraco.com/documentation/tutorials/Custom-Error-Pages/

This was added to the appsettings

"Error404Collection": [
          {
            "Culture": "default",
            "ContentXPath": "//errorPages[@nodename='404']"
          }

But returns the following error:

Could not parse xpath expression: //errorPages[@nodename='404'] System.InvalidOperationException: XPathValue must be an XPathNavigator or a string.

This has been working for months and has seemingly broken after a recent umbraco upgrade to 10.2.1. Parsing the error page by the page content key still works.

Any help or comments appreciated