I just failed this agent mission with a 100% displayed chance of success.
The percentage displayed is Affinity, not chance of success.
Affinity is the sum of chance of success + outstanding, if they add to 100% it shouldn’t be possible to fail.
The Streaming Ones February 23rd, 2018 - Summary (Agent system) this livestream
Exactly this. It’s the only time I’ve ever failed anything showing 100%, so I’m suspecting that whatever it is that makes the mission only doable by Jeronimo has some unintended side effect. I’ve run this mission several times and never failed it until now. I know that’s not a lot of sample points, but nobody I know of has failed it at 100%, either. Seems like it might be rare? I dunno.
If I were a betting person, my money would be on “rounding”.