If your HDMI cable is not connected correctly with the Roku device, it will give this type of problem so make sure cable is connected correctly. Reconnect cable from both Ends.
If you are using an AVR or HDMI Switch, then you need to disconnect it and directly connect HDMI Cable to your T/V Roku device. Try to change the HDMI port. If still, you are facing the same issue that changes HDMI Cable.
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