I own a Roku 4 and aside from the numerous other problems mentioned by others in the forums (youtube not working, various other apps not responding at all, etc...) I am having a problem with system update.
When I attempt a system update, it appears to start normally (circle spinning showing 'checking for new software')... After 20 seconds or so the spinning circle freezes... the Roku becomes non-responsive, then the roku reboots on its own. After this reboot, half the time the roku reappears back to the normal main menu; while the other half of the time the screen goes totally black and the roku is totally unresponsive.
Try a Factory Reset: Settings/System/Advanced system settings/Factory reset
(or hold the reset button for at least 30 seconds with the Roku powered on)
You'll need to set it/apps up again of course.