trynd ult bugs

I dont know how it happens but sometimes the trynd ult doesnt work. It will do the undying rage scream and it will go on cooldown but he will still die. It happened to me once but i thought i was just trippin but it happened again today during a ranked game with a trynd that was on my team. i really dont know how it happens i just know that it happens, just want to bring it to your attention.