A URL that renders a 'Redirect' HTTP status code of the 3XX series is still being referenced in an XML Sitemap.
Why is this important?
Your sitemaps should exclusively feature URLs that you want search engines to crawl and index. Only include URLs in your sitemaps that yield an HTTP status 200 (OK), are indexable, canonical, and not duplicated.
Search engines may begin to question the credibility of your sitemaps for crawling and indexing if they encounter redirects, like 301 pages. This can lead to unnecessary work for search engines and send mixed signals about which URL should be indexed.
What does the Optimization check?
The Optimization will be activated for any internal URL which shows an HTTP status from the 3XX series and is listed in one of your submitted XML Sitemaps.
Examples that trigger this Optimization:
Take for example the URL: https://example.com/old-page, which has been included in an XML Sitemap.
This URL would trigger the Optimization if it were to respond with a 301 (Permanent Redirect) HTTP header response:
HTTP/... 301 Moved Permanently...
URLs with different 'redirect' statuses also cause this Optimization to trigger (essentially, any 3XX HTTP response).
How do you resolve this issue?
To fix this problem, simply remove all URLs that return a 3XX status from your XML Sitemaps. You should then add the final URL they redirect to, assuming the destination URL isn't already in the sitemap.