Google Search Console reporting only a small fraction of the URLs in my sitemap index have been discovered

Question

My sitemap index file does not show any errors on google search console, but it only shows 397 discovered urls whereas it should have been over a million.

Basically my sitemap index file looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <sitemap><loc>https://www.example.com/sitemap1</loc><lastmod>2020-09-14T04:38:25Z</lastmod></sitemap>
  <sitemap><loc>https://www.example.com/sitemap2</loc></sitemap>
  <sitemap><loc>https://www.example.com/sitemap3</loc></sitemap>
  <sitemap><loc>https://www.example.com/sitemap4</loc></sitemap>
  <sitemap><loc>https://www.example.com/sitemap5</loc></sitemap>
  ... (614 sitemap entries in total)
</sitemapindex>

What can be wrong? Do I have too many <sitemap> entries?

edit: This was actually working, I had over a million discovered URLs, then I added like 200 <sitemap> entries to the sitemap.xml and it "broke", meaning it started showing only 397 discovered URLs for the sitemap (coverage is unaffected).

Update: I reduced sitemap count to 450 and google started crawling 33 sitemaps in the index. Still not crawling all child sitemaps though.

Answer 1

In addition to Stephen's reading suggestion above, it has been my experience that Google's count of files in the sitemap rarely matches the total number of files on the site.

In my case, GSC only shows the count that existed when I first published my sitemap over four years ago. Meanwhile, every page that Google finds using other means like links and manual submission through GSC, rarely if ever add to the count GSC shows for the sitemap. While the a few pages shown in the report may change, the count is unreliable.

If I were to wager a guess, it might be that Google's count only changes when it finds a page via the sitemap that it couldn't find any other way.