Google’s John Mueller was asked about an error with Sitemaps files. The question was around Google not being able to fetch and read two of the few XML Sitemap files but those files are perfectly valid. John said it can be a lot of issues but there is a trick you can try.
If the issue is on Google’s end and the sitemap file is accessible and technically fine, then sometimes changing the URL and filename of the sitemap file might do the trick. John said it is hard to say without specific examples and to post those in the forums.
But he added that sometimes if you change the sitemap filename/URL, it can reset things on Google’s end and reprocess them from scratch. John said the new URL might “reset Google’s opinion” of the sitemap file. That might do the trick but it really depends.
He said this at the 52:49 mark into the video. Here is the embed:
Forum discussion at YouTube Community.