My only regret is that I don't have video. I was playing on PS5, which I think even has a function to capture the previous 30 seconds if you're on the ball about it. But the whole thing was so astonishing that it never occurred to me.
I was playing the current double-target on Sapienza. I believe the Congressman target was an old target from the first game, and that the second target was added to spice everything up.
I wanted to use the opportunity to play with one of the game's significant new toys: the Sieker, a gun that fires an emetic dart. I guess this thing actually got introduced in Hitman 2, but that's the one out of the three games that I didn't play all that much (after maxing mastery on every map in the first game and not having it carry over, I didn't feel like doing mastery grinding again, so I pretty much only played all the H2 levels once or twice and then stopped).
Anyway, it seemed to me that the Sieker would be a pretty hack way to get easy Silent Assassin ratings on these missions: just shoot the targets with a dart when everybody's back is turned, then follow them to the bathroom, murder them, hide the body, and Bob's your uncle.
So I did some test runs. It took me a bit to figure out that the darts have a big arc on them, so you have to aim above your target in some cases and can't be too far away. But eventually I got to where I was hitting the guy outside a cafe (the new target) consistently while hidden behind stuff. Then I'd follow him and choke him out--without actually killing him, so I could practice on the other guy.
Then I did a couple of runs on the Congressman inside the mansion. That wasn't so bad, either. He had a few bodyguards following him around, but all I had to do, again, was wait until everyone's back was to me, then shoot the dart into the Congressman, and once again follow him to bathroom. I did that twice, and finally decided I was good to go for real.
So, I dart guy #1. I follow him to the bathroom, where I choke him out, and then I snap his neck. No going back now. I go and get my mansion guard costume and head to the mansion, to the library room on the first floor where I'd practiced darting the Congressman. I wait a bit.
Finally my target walks in with his bodyguards. After pausing for a moment, he walks further into the room, and his guards start to follow. I'm behind them all. I pull out my Sieker, fire, and hit. I even hear a line of dialogue about needing to go to the bathroom or something like that. But the guy doesn't really pause like they usually do when they get hit with an emetic. He just keeps walking slowly in the direction he'd been going. And then...
He flies up into the sky.
I mean, he just suddenly seemed to rapidly float upwards, through the ceiling. I couldn't see him anywhere. He was just gone. WTF?
Then I notice his guards are moving. Oh, right. They're programmed to follow the guy around wherever he goes. So I decide to follow them, hoping they'll take me to wherever he ended up. That's what I do, and eventually they lead me to the roof of the mansion, just above the spot where my target had flown straight upwards. Then they sit there staring into space, doing nothing.
I waited for a few minutes. Nothing happened. I tried looking up at the sky to see if I could see him stuck way up in space somewhere. No dice. The target menu still read as one killed and one still alive... even though the second target was now completely out of my reach, through no fault of my own.
So in the end, I had to just quit and fail the target. I don't think there was any fixing that. I had locked in the first target, so there's no way to attempt it again. The game screwed me good and proper.
But... eh? I guess I don't really care? I had already gotten enough Silent Assassin ratings on elusive targets in past games to earn me all the rewards I could get from it (not the Suit Only Silent Assassin ones, but the standard SA rating challenges), so it wasn't really for anything other than pride. And I now have a story to tell about a really dumb bug. C'est la vie.
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FWIW I did a quick search and came upon this old video of somebody actually engineering 47 flying off the map. Based on how he got this glitch to work, I'm guessing I must have done something similar unintentionally with this NPC--interrupted an action of his at just the wrong time.