I was having same issue. Switched out hdmi cable. Problem solved.
Thank you, this actually seemed to help, not understanding why but it did🤷🏽♀️
i take it back, it only worked for like an hour
This thread is over 2 years old, with many Roku OS releases since then. You need to be more specific about your issue, perhaps even create a new thread.
What model Roku (model number, not name)? Is it with any specific channel, or is the screen flashing even on the home screen? Does it happen only when you start and stop playback of a video?
Changing screen brightness to Normal seems to have fixed my issue.