What happens if you disconnect the power to the nowtv stick and don't use the nowtv remote, does your JVC television work every time ?
If so, the next thing i would try if you own a smartphone is to download the free Rouku Remote Control App and use the App with the stick (don't use or press any buttons whatsoever on the nowtv smart remote controller).
Should the Roku App work directly off your phone without switching off your TV.
Then the next thing i would try is going into the stick menu settings under Remote Control and disable the power standby & volume adjust buttons feature (either ignore the music prompts during the setup or when getting to picking a TV brand select another manufacture rather than JVC to see if there is some sort of infra red code clash with the stick remote and your JVC TV).
Then try the nowtv stick and the nowtv remote again with your JVC television to see if it makes any difference.
The only other thing that i can think of to try is to go into the JVC menu settings and have a play around with the HDMI CEC control settings.
You aren’t by any chance pressing the button at the top of the remote to turn the NowTV Stick on when you want to use it, are you?
Get Samsung to put this in writing, and submit it to NowTV, with a request that they stump up for the TV repairs.
But I have to say that I have three Samsung TVs, all with a connected NowTV Stick, and nothing has gone wrong with any of them.
It must frustrate Samsung that their customers can’t just use the built-in NowTV app, but it is dog slow.