Thanks for letting us know what you're running into. Are you also seeing black flashes on your TV? Does this occur on any screen or only in specific channels? Does it happen when you play content, or anytime you are using the device?
Please feel free to send me a private message with your Roku account email address, the serial number of your device from Settings>System>About, along with any additional details about the issue. I'll help take a closer look and continue assisting you from there.