How did you manually enter HDR mode?
wondered that myself since nearly all TV's have to receive a HDR signal to do HDR!
You go to the picture modes and select the "HDR" mode. I have a Sony UHD TV. An 850C.
When watching HDR content it switches to this mode automatically. My XBOne S is working fine with HDR and UHD BDs. But I will still be using my Samsung K8500 as my primary UHD BD player.
I really like the 30%+ reduction in power. And I'm using the vertical stand. I had never placed any of my game consoles vertically before. I might do it with my PS4 now too.
I still need to give my info to MS to get the free Kinect adapter. That is really my only complaint right now. I can't stand navigating the XBOne S UI with the controller. I had always used Kinect before. It is so much faster using Kinect to naviagte than using the controller.