Just repeat the steps from my post above, which is in this thread. Clearing the cache restarts the Roku. If you would just like to restart your Roku TV, go to Settings/System/System restart/Restart.
A shortcut that people in this thread have done to restart their Roku TVs is to unplug them for a couple of minutes, but it's better to restart or clear the cache instead of having to constantly unplug your TV every time you encounter this issue. If you decide to unplug as people have done in the posts above, then make sure you're on the home screen and it's not on a screensaver before turning off the TV and unplugging it.
Your best bet if you subscribe to Prime is to contact Amazon and let them know your TV model is still having issues, and they may be able to correct this for you.