Google might be having some weird bug with XML sitemap files that have hyphens within the final name. So if your sitemap file name is /sitemap-10.xml it will trigger a “couldn’t fetch” error, but using /sitemap10.xml with the same exact file will not trigger any errors. This error shows up in the Google Search Console sitemaps section.

This was uncovered by the folks at Screaming Frog who posted this on X:

Google did not yet respond to this issue, but Screaming Frog did send this screenshot:

Others were also able to replicate this:

Do you have this issue too?

Forum discussion at X.