I beat all stages from start to finish without changing difficulty ever and I got all difficulty achievements except Supersoldier. I even went back to mission select and all of the highest difficulties I beat them on say Super soldier.
If you go through the missions list, it will tell you the time, souvenirs, and difficulty you have completed for that map. You should try to get a photo showing your full completion as proof.
The same thing happened to me. I've beaten the entire game on Supersoldier, and I didn't get the achievement. Let me know if you figure out how to fix this.
I initially didnt find this interesting. Just laughed with the topic. But seeing that the user has been asknig for help and Crytek is really ignoring another problem they are responsible for torwards their consumer pisses me the f off.
nobody is going to help you. there is no help. you didn't get your "achievement" and it's not like Crytek is going to remotely access your xbox and plop the achievement into your dumb little list of achievements. just... move on.