Replay code: 61ZH0K
This is the third or fourth time I have experienced this, but the first time I went back on the replay to check. The ultimate animates, and then detonates but does nothing to nearby enemy players. No hit marker, no registration, nothing.
I’ve played her a bit and yeah I’ve found her ult to be an odd one, from both sides to be honest. But like you I’ve had games where I couldn’t ult anything even though it seemed like we were right next to each other, or like it should’ve hit them.
Per the hero info tab, Panopticon has a travel time. So it must be a moving projectile, and from what I can gather, that little sparkle radius is not especially generous. It unfortunately only gives us info on the barrier that results from that little sparkle hitting an enemy. It would be nice to know how wide the activation radius is, but without that information it’s a matter of trial and error on the player side that eventually becomes muscle memory. It will travel in a straight line entrapping every enemy in that path until hitting an obstacle which stops the ultimate, and from shooting one off into the horizon in the practice range it seems like the travel time is indefinite, until it hits a hard surface to stop it.
I watched the replay and from what I can see, in the two Domina ults, neither of these connected. In the first case, the only one to possibly be hit would be the Reaper, who was just out of range of the projectile. The sparkle actually hits the ground right behind him as he is walking back down the ramp, and you can see how the blue radius of her ult’s activation sparkle is not close enough to him to justify his imprisonment.
And in the second case, I think it could be one of two things. Either you aimed it at the floor, which stopped it right away, or the Doom might’ve ate it. If you take a look at the opposing Doom’s perspective you’ll see his perks include power matrix, ie “block absorbs projectiles for the first second of its duration.” Now I’m not a Doom player so idk how this actually works, and if you look at his POV the block meter doesn’t seem to go up from eating it so I’m not sure if that’s always how this perk works or if that’s a bug (and any Doom players out there who could lend their expertise, I’d love to know what you think!), but it’s possible that Doom simply absorbed it. But watching from Domina’s perspective, it looks like she aims it at the ground and it explodes just in front of his feet, meaning he wouldn’t have been affected.
Her ult is weird. That sparkle doesn’t do anything but activate the imprisonment barrier, and it’s that barrier that damages enemies. You want to be aiming it not necessarily upwards (unless you’re aiming for an in air target obv), but maintaining line of sight with the folks you want to catch. Both times here you aimed it downwards, which would work if the imprisonment was activated by the sparkle detonating. But instead, what actually happens is that if that little sparkle touches an enemy, they will be imprisoned in a barrier. That barrier will then do 100 - 300 explosion damage depending on its health. So aiming down will only catch someone who is under you, and most times will result in the activation sparkle of her ult just immediately deactivating from hitting a hard surface, like I think may have been the case here. I’ve been there too 
And even when I aim it at a group thinking wow cool I’m gonna hit 5 people for this achievement, then it’s actually just one… or none >.<
Seeing it successfully go off into a multikill is really satisfying though, but I think her ult could use something. Idk what but something, considering it can be whittled down into nonlethal damage. It would be neat to see it bounce from one target to the next or something, rather than only hitting targets in a single file line. But that’s what we’ve got right now, so the best advice I can give you is to look upwards a bit and give that a shot, see if you feel like you are connecting more ults or not. Have fun!! Was really satisfying watching your tracking in first person thanks for letting me take a gander 