Originally Posted by Gentlemane
Same thing always happens to me (ok, not always, but from time to time I find myself in that situation)
It happened with Ziggs ultimate once too, but even manually clicking the ultimate didn't work (while on Malz worked... sometimes).
Dunno how to replicate however, try inside a hetic teamfight with lot's of things on the screen (minions, projectiles, spells, effects, champions with large frames and/or sparky particles...), I thought it was something regarded to lost packages, bad connection, lag, my old battered video-board... but I think I was wrong
This sounds the closest situation, cuz its only when its 4 ppl+ in the fight, but it won't work forever like it did go off, but no cd? like it just wont work, idk maybe its because you die during ult, it happens after?
So yeah try that, dieing while getting ult'd, then come back and try and ult, after cool down comes up and it's available, (only smart cast )