My Roku ultra restarts while using Netflix, youtube, prime. I havent tried all other channels yet. There is no consistent time frame of how long on a certain channel. Just seems to restart randomly while watching. I just set up the Ultra a day ago. I tried to restart the Ultra to see if that would help but it doesnt seem to be working. I also checked to make sure the latest update was used as well.
I have a Roku 3 which is doing the same thing arbitrarily restarting, mostly while in the Sling App. It has done it on its own and when I trying to go back 1 screen from the 'Guide'. Started doing this last 2-3 months. Had no problem prior to that!?!
Try removing the channel(s) from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel(s) back once more.
Does this clear up the issue you are seeing? Please keep us posted and we will be able to assist you further.