Use Several Smaller Sitemaps to Locate Indexing Issues
Having several smaller sitemaps for the different sections of your site is recommended for diagnosing indexing issues.
URLs in Sitemaps Are Not Guaranteed to be Indexed
Google may choose not to index URLs in sitemaps that are very similar to ones already being indexed and if they differ to the ones linked within the site (e.g. trailing slash/non-trailing slash).
Mixed Migrations May Cause Google to Index HTTP or HTTPS URLs
Forgetting to update your sitemap files following a HTTPS migration could cause some pages to be indexed with the HTTP URL and some HTTPS.
Video Sitemaps Can Specify Countries Where Content is Available
With a video sitemap you can define which countries your content is available, which is used for video search results.
Low Proportion of Indexed Pages Points to Technical Issue
If a site has a low proportion of indexed pages, this usually points to a technical issue than a quality issue. Compare the site map index counts and index status report for differences. Try splitting up sitemap file , checking indexed pages using info: query, that rel canonicals match those in sitemap file, hreflang and internal linking. Also, uppercase, lowercase, trailing slashes all matter. Then check crawl stats to get idea of crawl rate and if it’s reasonable.
GSC Sitemaps Report Can Take Couple of Days to Update
Sitemaps report in GSC can take a couple of days to update after changes have been made to the sitemap and may explain why non-existent errors are reported.
Google Validates Sitemap Files Immediately After Submission
The 50k URL limit for sitemaps is based on the number of entries or elements in the sitemap file (including alternate linked URLs) and this is validated immediately after they are submitted. So if there are too many URLs in the sitemap file, you will be made aware of that straight away.
Submit Sitemap With Updated Last Modification Date For Faster Crawling of Updated Pages
Submit a sitemap file with an update last modification date to speed up the process of crawling and indexing of pages that have been changed.
Ensure Separate Sitemap Files Don’t Contain URL Overlap
Having separate dynamic and static sitemap files is fine, as long as there is no URL overlap.