Twitch Ultimate (Nexus immune to damage!)

When Twitch uses his ultimate and attack the Nexus with only the middle lane towers and inhibitor destroyed, the Nexus is 100% immune to damage. Not low damage dealt NO damage dealt at all after attempting numerous attacks. Twitch can still target and attack the nexus, just zero damage.

Almost lost a game and looked like an idiot trying to back door as Twitch when I encountered this bug yesterday.