"HDR10+ is currently limited to Amazon Prime Video on select Samsung TVs and a limited number of Ultra HD Blu-ray discs including Bohemian Rhapsody and Alien 40th Anniversary, but we’ve been unable to conduct our own tests of the format. We have, however, seen the tech as presented to us by Samsung and Panasonic. While demos such as this can’t be relied upon to draw firm conclusions, they’re certainly enough to get us excited."
That's all I can find on the matter. I would assume that there are limitations, perhaps that the video or film selected is not formatted to HDR10+