I have the same issue with my Ultra. I have a new tv and yesterday, it just started flashing to black. I contacted customer support and they had me reboot my roku ultra, my tv and my router, all of which I had done prior to our chat. I did it again with the rep and had no success, again. My tv is smart and the same apps that I also have on my Roku, work perfectly on the smart tv. The Ultra is less than 6 months old. What gives? I also changed the HDMI cable with a new one!
@denny1949 your problem is not what this thread is about. This is referencing a Roku TV, while you have a Roku Ultra. But I must also ask, what make/model TV and what model Ultra do you have? There are numerous reports of flashing screens with LG OLED sets and the Ultra 4800.