There may be several reasons why a sitemap is not showing all links:
Incorrect Sitemap Structure: If your sitemap isn't formatted correctly, search engines might not be able to read and understand it properly.
Sitemap Size Limit: There's a limit of 50,000 URLs or a file size of 50MB uncompressed for a single sitemap. If you have more URLs, they won't appear.
Exclusion in Robots.txt: Your robots.txt file might be blocking some pages from being included in the sitemap.
Noindex Meta Tag: Pages with a noindex meta tag are often excluded from the sitemap.
Orphan Pages: These are the pages that are not linked from anywhere on your website. Since sitemap generators crawl from one page to another, they might miss these orphan pages.
Here are some possible solutions to fix the error:
Ensure Correct Sitemap Structure: Validate your sitemap using a sitemap validator tool to ensure it follows XML schema.
Split Large Sitemaps: If your sitemap exceeds the limit, split it into smaller ones and use a sitemap index file to manage them.
Check Robots.txt: Review your robots.txt file to make sure it’s not disallowing the URLs that you want to include in the sitemap.
Review Noindex Tags: Remove noindex tags from important pages that should be in the sitemap.
Link Orphan Pages: Find orphan pages and link them appropriately from other pages so the sitemap generator can discover them.
By following these steps, you should be able to ensure all desired links are included in your sitemap.