No worries. In fact, at least one time in the past I noticed a similar error, but I don't recall if it was from my RSS feed or someone else's.
Thank you for your kind words about the article, as well as pointing out that erratum – much appreciated! I will fix that right now.
Take care and thank you for all the work that you're doing on Drupal!
Thank you for contacting me. I verified that the link worked yesterday evening when I published the article, and verified it again just now: https://www.ross.ws/?_writing/articles/Proprietary%20vs.%20Open%20Source.... Neither time did I see any report of a failure due to an unsecure connection.
Also, it showed up fine this morning in my general RSS feed (https://www.ross.ws/_rss/rss.xml) and my Drupal feed (https://www.ross.ws/_rss/rss_Drupal_Planet.xml).
Like so many owners of modestly-budgeted websites, the security certificate I'm using is Let's Encrypt, provided by the hosting service, SiteGround. I can't imagine that could be causing the problem, as it is such a popular option.
Does the problem appear to be specific to that article? Or is it affecting all of my Drupal articles in that feed?