My Roku Ultra screen intermittently flashes to black while playing YouTube TV. In most cases, audio continues in the background. If Closed Captions are enabled, the screen still flashes black, but the captions remain visible as the program continues. These blackouts usually last less than a second, but on rare occasions, they persist for several seconds while audio and captions continue just fine. I'm also now experiencing audio breaks and dropouts while using Pandora, which I suspect is related. These issues appear to have started following a recent software update: Version 14.5.4, Build 5944.
