Just realized that some of the Kindle e-books I have gotten for a little over a month now I could no longer open in other e-readers or apps. On books I own I believe I have the right to read them on the device I prefer and like to back them up in a way so that my access to my books is not controlled by some third-party which might go away. Anyway, I use the Calibre e-book management tool and have some user-created plugins installed which normally automatically strip the DRM from books I own when I import them into my Calibre library. This apparently had stopped working.
It’s been a long time since I installed these plugins and apparently something had changed in the Kindle DRM. I downloaded the most up to date version of the DeDRM plugins, then re-installed them into Calibre. I then removed the DRM locked books from my Calibre library and re-imported them and everything is golden again. Apprentice Alf’s blog continues to be a god send.