Rengar does not autoattack

I used my ult. I jumped on a Cassiopeia. I used empowerd q right before i jumped and used hydra while in the jump. When i landed the empowerd q did dammage. After that i was unable to autoattack the champion. I was also unable to move. I'm not sure but i might have been unable to use abilities. I had gostblade, hydra, mercury treads, randuins omen, last wisper and black cleaver. I died a couple seconds later and when i respawned i could move again. This happened several times in a row in two different games. Edit: It happened again, except this time i did not die. After about 3 seconds i could move again and everything worked fine.