For whatever reason, for the Scourge path, the lesson for three rmb into 4 does not give enough orbs to complete the combo, and it gets angry and resets anytime I try to get the necessary amount of orbs. Here's a screenshot including the greyed-out skill icon, registered key presses, and insufficient orbs. https://imgur.com/66IyaY4
And yes, I am hitting the mouse buttons quickly in succession, I tried several speeds and rhythms.