Could you tell us more or walk us through the issue you're experiencing? A photo of the problem showing on your TV screen would be a great help as well.
Also, please provide us the following information for further investigation:
-Roku device model -Serial number -Device ID -Software OS/version (these can all be found in Settings > System > About) -Tracker ID when this issue occurs (when you see this issue occur, press the Home button 5 times, followed by the Back button 5 times) -Steps to reproduce the issue you are seeing
With more information, we will be able to assist you further.