There is a small chance that a mini-game will not reward you anything after you play the game and reach the required amount of points for whatever you are after:
Skullriders you only need about 330 points to get full mana, After reaching 570 points it rewarded nothing.
Stun is sometimes not affecting average on the street enemies: In Marleybone I stunned a deadly scratcher but it was able to cast a myth spell, but it fizzled.
That happened to me a few times when I played Conjuration. It probably has something to do with a brief disconnection, and the server not crediting you with the right score because of it.
