There were reports of people never seeing the result screen and receiving the rewards.

Do you use PS4's rest mode? Try turning off the game completely and booting it back up.

I'm on Xbox one. I think I saw the results screen but never even got the kill reward. I got the obscene amount of koins though.

Since you're still part of the Lin Kuei I'm assuming, try this input when it says "Finish Him/Her" and see if it unlocks -

(Screen length/far distance)

Hold R2, Up, Up.

I know you said you're on Xbox, so just hold whatever the equivalent of "R2" is on Xbox.

Otherwise, you're not the only one it didn't unlock for. Hopefully they'll fix these issues as well as others people have been experiencing with the factions and online play.

Were you part of the faction, and did you contribute at all to the faction invasion, at the time that the Lin Kuei was victorious? I got it as soon as the Faction War ended (I was actively playing at the time).

Yes to all. I helped with the invasion boss, did an invasion tower, fought an assassin or two..