Using Ansible and my own internal monitoring, I quickly found that servers were fine, but DNS was all out of whack.
It looks like globally, many of my domains had invalid or missing records. And locally, using either my ISP or Google DNS, I would get responses sometimes, other times no. See, for example: https://www.whatsmydns.net/#A/www.hostedapachesolr.com
I use Name.com currently, mostly because they're not GoDaddy (who I used 10-15 years ago, but never liked), but I'd like to move domains to a more reliable and transparent company... Name.com never seems to respond to tickets or Tweets in a timely manner, and when they do (a day or more later) the problem seems to have resolved on its own.