Did you try another power source for the Roku stick? Or another Roku?
I'm not suspecting it's a network speed issue since you wrote it's going off. As if the power went off. If it is slow WiFi which is very common be sure the router is 20 feet or less to the Roku.
We've had Roku for 2 yrs and all of a sudden it's going off frequently or not coming on at all. We get error message 019 and 403 forbidden. And "no internet connection" when we do have one. We've also seen "Slow or no download speeds" but when I check, it's 16 and we pay for 20 mbps so it's not bad.