Generally Samsung apps are poorly designed and unreliable. I keep having this problem where I am not able to install any app and there's no error coming out telling you what the issue is. However, there are 2 inconvenient workarounds you can try to recover the useless Smart Hub app.
1. Shutdown your TV and then power it OFF (unplug from power source).
2. Reset Smart Hub (Not recommended as some of the apps will be uninstalled automatically)