We would be more than happy to investigate this issue for you.
Can you please provide us the following information:
-Roku device model, serial number, device ID, and software OS/version (these can all be found in Settings > System > About)
-does this issue occur on a specific channel? if so, what channel and what version/build is the channel (this can be found be selecting the channel on the Home screen and pressing the * button)
-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
-did this happen after the latest update
-do you hear audio when you see the black screen
-would you be willing to send us a video of the issue you are seeing
-have you tried connecting your Roku device to another TV to see if you are still seeing this issue occur
Once we have this information, we will be able to pass it along to the appropriate Roku team to look further into.