The specific error code "1871" in an XML sitemap is not a standard error code recognized universally. Error codes in XML sitemaps typically vary based on the software or platform you are using to generate or parse the sitemap.
To diagnose the exact cause of the error, you need to refer to the documentation or support resources provided by the tool or platform you are using to generate the sitemap. Check the error code against the tool's documentation to gain insights into the specific issue being flagged.
If you provide more information regarding the software or tool you are using, it might be possible to offer more specific assistance in troubleshooting the error.