Me and my buddies completed the campaign in about 2 hours and 15 mins. Out of the four of us, I’m the only one to not get the achievement. I’ve done all the cutscene missions on legendary as well. I’ve looked this up before and have been trying various fixes like restarting my game and replaying Noble Actual, but nothing has worked. So as of right now I’m not sure what else I can do.
According to your service record here on Waypoint, the Epilogue and Lone Wolf did not register. Watching the Epilogue again on Legendary and letting yourself be killed on Legendary on Lone Wolf should unlock the achievement.