Thanks john of MT for the test. I'll continue to troubleshoot.
Whatever it is, it's substantially worse over the past few days. I keep my (Windows) OS on automatic updates, as well as my browsers. So thing are shifting all the time.
I'm at a point where things fail more often than not. The video stalls forever if I jump forward in time, and when I expand the video to be full screen. I eventually stumble my way through using page reloads but I'm spending more time wrestling with the playback now than practicing