I can CONFIRM this is a new problem. I bought two Roku Ultras last February and everything was fine until a week ago, now when watching I get the flashing black screen for a few seconds, followed by the "Dolby Vision" logo re-appearing. Turning off Dolby Vision in settings and choosing just HDR fixes the problem. And yes, I did EVERYTHING else to fix it. New HDMI cables, different HDMI ports, tinkered with HDCP settings, lowered OLED backlight, rebooted unplugged etc etc. I know this a ROKU issue because one of my TVs runs through a Pioneer VSX-1131 to an LG OLED, one of them runs directly from the ULTRA to an OLED LG TV, and my third OLED LG TV is not connected to anything and has no issues with flashing screens when running Netflix, YouTube TV etc directly from the TV Smart Hub, only the LG OLED TVs connected directly to an ULTRA either directly or through a receiver have this flashing black screen Dolby Vision problem which appeared a week ago after three months of no problems (v10 issue?), ROKU please fix!