I was playing King’s Row. There was an enemy Junkrat by himself - no allies near him - on the roof of Defenders Spawn A (not sure location matters - that roof over the tunnel, before the first payload checkpoint, off to the right).
I was playing junkrat on attack. I cast my ult about a second after I heard him cast his. I drove my tire right up to him, climbing to the roof and seeing his character crouched in the ult position. I detonated my ult right on top of him. He didn’t die, I assume it did no damage. There was no countermeasure on him, like Baptise or Ana Nano or anything like that. My ult just did 0 damage, should have easily killed him.
On a possibly related note, there was another instance in that same match where I detonated an ult on top of another player - a Zarya who did not have bubble. Similarly, did not kill her damage even though the ult detonated - I’m 95% sure she didn’t destroy it. So may be a more pervasive junkrat ult damage problem.