@fusionaddict – I didn’t do anything special, honestly to start getting it to work. It just started working.
In the dashboard:
Appearance
Customize
Post Information
Featured Image
Scroll to the bottom of the options where it says “Use featured image in header” and select enable
I did log out and log back in (to reset a different issue) and then it began working for pages as well as posts. I wish I had a special trick to share. It was just one of those things….