An inclusion of a URL that gives back a 5XX HTTP status error in an XML Sitemap was detected.
Why is this important?
Your XML Sitemap should be composed of URLs that you intend for search engines to crawl and index. Ideally, these URLs should return a 200 HTTP status, be open for indexing, represent the primary version of a page (canonical), and not be repetitive.
Should search engines come across errors such as 5XX status pages within your sitemaps, their reliance on these sitemaps as cues for crawling and indexing could diminish.
During an interview with Eric Enge, Duane Forrester, then with Bing, implied the importance of clean XML sitemaps; Here's that insight:
What does the Optimization check?
Any internal URL that causes a 5XX HTTP status and is found within any submitted XML Sitemap will activate this Optimization.
Examples that trigger this Optimization:
Imagine the URL: https://example.com/page-a is part of a submitted XML Sitemap.
Should this URL result in a 500 (Internal Server Error) response, the Optimization would be activated:
HTTP/... 500 Internal Server Error ...
URLs returning other ‘server error’ statuses, synonymous with 5XX responses, will also initiate this Optimization.
How do you resolve this issue?
Labeled 'Critical' due to its potentially devastating impact on organic search performance, resolving such issues should take precedence on your priority list.
5XX errors highlight server-side problems, not just issues with your website's content. They inhibit both user and search engine access to your site, warranting immediate troubleshooting, possibly with a developer or server admin to pinpoint the cause.
Post resolution, ensure the XML Sitemap remains devoid of such errors.