Tryndamere's ult goes off and can still take fatal damage.

Hello, currently Diamond 3 Trynd Main so I have a lot experience with his ultimate being bugged. I originally thought that it was the corrupting potion that was bleeding through Undying Rage and killing me but that's not always the case as i have died moments after activating it for no apparent reason. This is something that happens about once every 8 games for me. To clarify 100% i successfully activate my ultimate and then die 1-3 seconds after its being used, i'm well within my time limit and even the enemy will note it in all chat.