Wukong Ult Reset

i was in hexakill, i was about to go in on a veigar and when i jumped in my ult was off cooldown, i casted it and nothin happened except the ultimate got its cooldown set back up to 10 seconds. little to say other then i lost that fight. and it wasnt lag, my pc runs league very well, it wasnt latency iether, i run a straight 44ms and everyone else was moving too