Yeah, I encountered several problems with HDR and working from an engine at work as well. For example, there needs to be a handshake between the nvidia control panel, your game engine and the TV and for some reasons that thing can break on many different occasions.
I had problems for example when my gameview window on the TV was not forced to focused full screen. However, when I tried navigating the viewport on my main screen, the viewport on the TV got out of focus and thus HDR broke immediately.
My nvidia driver looks like this for the Samsung HDR screen and as long as that viewport is fullscreen and in focus I can have it working but I havent tried it in Unreal yet, but the driver setup should be the same
