Not sure how that is occurring for you but I can assure you that mpv (the backend player engine for PMP) is not capable of passing though the HDR metadata correctly. Your system (assuming its Windows here) is doing something that triggered the HDR signal from the OS but mpv can not capitalize on that yet. There was some work late 2018 by one of the mpv devs Jeeb to get that working in Windows. However that work is not complete and there has not been any work for HDR on the backengine of PMP for well over 2 years.
