Twitch Rat-a-tat-tat Damage Bug
When Twitch activates his Ultimate- for the duration of the ult any basic attacks done to an enemy nexus is negated. No damage indicators are shown on particle contact although the animation still completes and the piercing is still shown (Unknown if enemies are damaged by the piercing round behind the nexus). Damage is returned to normal once the duration of the ult ends.
TL;DR When twitch ults a nexus, damage isn't done to it until after the ult duration ends, meaning all attacks are set to 0 damage until the effect ends.