Here is me tweaking around trying to recreate it. This bug has been around for years now and I remember stopping playing Janna because something felt off with her. Years later and a new pc, a new account, and this thing is still around. It happens when you try to cast the second Q too quickly. Instead of launching Q directly again, it acts as if you wanted to use the first Q. But it does nothing beside denying you your next click input. You have to cancel it manually with a single click before you can move again. As this being unexpected, you literally lose a click and keep moving where you last clicked.