The situation occurs when a URL yielding a 4XX HTTP status is discovered within an XML Sitemap.
Why is this important?
Your XML Sitemap should solely encompass URLs that you intend search engines to crawl. Only URLs that respond with HTTP status 200 (OK), are indexable, canonical, and distinct should be included in the sitemaps.
When sitemaps contain errors like 404 pages, search engines might disregard sitemaps as credible crawling and indexing sources.
What does the Optimization check?
This Optimization is activated for any internal URL that provides a 4XX HTTP status and is listed on any of the submitted XML Sitemaps.
Examples that trigger this Optimization:
Take as an example the URL: https://example.com/page-a, which is included in an XML Sitemap.
This Optimization would be prompted for the URL if it resulted in a 404 (Not Found) header response:
HTTP/... 404 Not Found ...
How do you resolve this issue?
This Optimization is deemed 'Critical' as it points to a severing issue, with the potential to significantly hinder your organic search presence. It is imperative that these Critical issues be managed with urgency.
Eradicate any URLs with a 4XX response from your XML Sitemaps to correct this issue.