Word of warning to anyone following along with an old version of Unity: In 2017.3 Time stays frozen until you manually assign the timescale a non-zero value in the editor (or restart the game).

What do you mean by manually assign a non-zero value? If you set the time scale to 0 you can stop time altogether, which is useful for a pause menu. Are you not able to reset time back to 1 (or higher than 0) from script afterward? 

That's exactly what I meant, but was having a hard time finding the right words for. To reiterate: if I set time to 0 using the script (with right click),  left and middle click stopped working. In versions after 2017.3, it works fine.