Just for reference the on / off button at the top of the nowtv smart voice remote controller is for switching your television on or off from standby and is not designed for switching on or off the stick has you have found out.
If you have the 1 touch feature on the stick ticked in the stick menu settings (default), then one press of either the home button, back button, direction button or OK button on the nowtv remote controller will automatically switch your television to the correct HDMI input source connected to the stick ready to watch.
Should the 1 touch feature in the stick settings be disabled, then you would have to select the HDMI input source on your television remote controller to see the nowtv homepage screen.
I have the same problem with stick and haven’t watched NowTv for months. Would cancel if they hadn’t given me two months at £1.50!
I ha e had to do the same thing, turn off at socket, wait, then try again. Sometimes it take 3 attempts. I have a Samsung.
I note the blue light flashes when not working and is steady when it does. Changing HDMI ports makes no difference.
I wonder if the box would be better?