Not only can this trophy glitch. You may have to delete your game and kill an enemy/complete a quest for it to pop. Or level up again. On top of the that though, the f***ing XP for killing enemies can glitch. In the sense of, you might get 0XP from a lvl80 Deathclaw. Or even 0XP for launching a nuke. So there is that aspect to it. I apologize for my anger, but there is not many worse things then getting 0XP from lvl60+ enemies or from a hard event. Finding a new server can fix it, or restarting the application. Watoga is really good for grinding XP or doing the quest for launching a nuke. Here is my video guide on how to grind XP.
Also save some quest trophies for after reaching lvl85, as the game gets really boring (at least for me) if you only have this trophy left. Take care! -KC