[GAMEPLAY] Bard ult not doing anything sometimes

Hi, I just played a game as Bard, and there were 2 times when I ulted enemies and it didn't actually do anything to them. I'm not really sure what steps you could take to reproduce the bug, as it hasn't happened to me in any of my games before.

One of the ults was aimed at Baron Nashor and two enemies that were nearby, and it failed to affect either Baron or the enemy champions, and the other time was at the start of a teamfight; one of my team's bruisers got caught out by Sion ulting into him (perhaps that had something to do with it, but I know Sion isn't affected while ulting), and I ulted just behind my ally on the enemy team, hitting 3 of them with my ult, and again, it didn't affect any of them (it hit the enemy Cho'gath, enemy Bard, and I believe Sion as well -- again, I understand Sion's spell immune while he's ulting, but he'd already hit my ally with it, but maybe the immune effect lingers for a small bit of time after he finishes). The second instance had the enemy Bard ulting my ally a little bit after I had ulted. The area he cast his ult on was slightly ahead of my ult, but overlapping a small bit. His ult worked, but mine failed to do anything for some reason.

Again, not sure really how to reproduce this exactly, since it occurred at 2 different times in this specific game. Perhaps it had some weird interaction with the enemy Bard or Sion because of their ults, although I'm not sure.

Thanks.