I am updating this, and hopefully adding information that will be useful to others.
I discovered that in the Yoast SEO plugin, there is also a sitemap generator and I had that turned on. I’m not entirely sure how I had 2 sitemap plugins working at the same time, but the Google XML Sitemap, because its sitemap is called sitemap.xml, is the one that I had submitted to Google Webmaster Tools. Well, around March 20 it stopped updating. The “old version” with all the individual posts (through March 20) was what was shown with the “www” prefix. Without the www, there was a lot of sitemap-related text, but no hyperlinks.
I disabled the Yoast Sitemap, but since there is no “generate sitemap now” option in the Google XML sitemap plugin, it appeared as though nothing had changed, so I wrote my initial post.
After 24 hours, I looked again, and the Google XML sitemap generator is working as advertised.
