Gameplay. Twitchs ult on nexus doing 0 damage

I was just playing a game as twitch and went to backdoor the nexus. When I walked up to it I hit R and started shooting. 0 Damage was dealt. I even tried moving up a tad to see if maybe my ult out ranged me and nothing still. I dont know if this happens a lot but I just had it happen.

1. Hit Ratatta on twitch
2. Walk up to Nexus
3. Char stops walking when in range to shoot and does 0 damage.