I've had my NU7100 for about 9 months now, and I kept hoping a firmware update would fix the HDR functionality. So far, no luck. Since the warranty is about to expire, I'm now reaching out to Samsung for help. I have a JU7100 that has an overall acceptable HDR display, so I know what to expect. The NU7100 seems to get darker and duller when HDR content is played. It doesn't matter if I use the TV's built in DLNA player, my Roku Ultra or Nvidia Shield. When playback begins, the screen noticably darkens. This is the exact opposite of any other display I've ever seen with HDR content. I have a number of test videos, as well as HDR 4K movies, and they all display the same. The only content that seems OK is a single HLG test video.
I'm waiting for Samsung to confirm my warranty status, but in the meantime I wanted to see if anyone has any ideas.