I came upon this community looking for help with my tcl roku flashing dark on one side. I have noticed that a lot of people are having the same issue. I reset my roku and it was ok for a half an hour and then started flashing dark again. Terribly long story shortened up i went in to settings and changed the picture setting to normal. For some reason it was on bright after reset. It has been 24 hours and it hasn't flashed dark. I hope that this helps someone.
Actually, this looks more like an issue with Dynamic Contrast. I know that on my Sharp TV, I would occasionally see odd abrupt brightness changes (full screen) until I turned Dynamic contrast off. And so, I would suggest to those seeing this particular issue, turn off Dynamic Contrast and see if that fixes the issue.
Now, since Dynamic Contrast would appear to be a function under control of the Roku software, another problem that seems to need solving is the habit of Roku technical posters to just point people with problems to the hardware manufacturer, instead of attempting to truly isolate, understand and then correct the problem.
Perhaps you could point to my previous paragraph as a "Solution" and Check mark it accordingly.
It may be as you say, but, with the litany of mis-functions, malfunctions and interruptions of normal operation of the sets induced by software "updates", I would suspect that memory leaks or buffer overflows within the Roku software is adversely impacting the operation of the processor chain which runs the TV. In fact, I would make book on it.