This happened to me too, and I probably spent way too long trying to recreate it. Truth be told, nothing in the code really looks like it would cause this issue. My best guess is that when the game is in the ready state, for some reason getWordOfDay() is called every frame, and maybe switching tabs causes some desynchronization.

Also I think the game defaults to easy mode when you open it for the first time, but the switch does not indicate this properly. I think it's bc line 72 isn't supposed to make the equality check to "true", since it can only ever take bool values anyways.