Hey, I have a problem. I finished Reach in 2h58min on Legendary, but I do not have the success nor the nameplate 
Help pls ! 
Btw I’m on PC (Steam)
I didn’t get it either when I did it, but to unlock it I ended up starting up the ONI Swordbase mission on Legendary and then turned on competitive scoring and it popped as soon as the mission started. Also make sure that the enemies kill you on Lone Wolf and you don’t kill yourself.
Well, Lone wolf doesn’t count as a mission for the achievement. I started again some missions and multiplayer games but nothing happend…
I will just wait 72h and if nothing is fixed I hope the support will unlock it for me.