That sucks, but yeah I've had the ult misfires happen to me as well. I've also had a rat tire blown up before it even spawned on my screen to drive. Again, I'm the one who isn't lagging so this doesn't even make sense. I have had Hanzo's dragon deplete me to zero, then no dragon comes out. I think this is the closest to your situation. The audio cue played to full, meter went down, died and a dice roll said no dragon.
I don't know if this is intended and the game is telling the truth, if signals are getting crossed and it's just rng, or whether it's a bug and needs to be fixed. No idea. Again though, this happens few and far between...it's just that those situations stick out hard. Most of the time all of my ults work, times when me and an enemy double kill eachother seem accurate...example widow+hanzo, my arrow took time to travel so even though I shot first we both died.