This forum has well documented information regarding the freezing issues and I have tried them all but it still freezes 90% of the time for me
When completing the scenario missions I have had to complete the majority twice so it would save. The order for scenario mode is results --> achievement --> save.
On one occasion my console froze and I didn't get the achievement. I repeated the mission again and it froze however this time it unlocked. It is this issue that becomes a problem with the premium rewards.
The premium rewards follows a different process of results --> save --> achievement. After shooting down my second boss in big boss mode. My console froze and like has happened once before I didn't unlock the achievement. I repeated the mission but no achievement probably because it already saved that I have the plane unlocked.
As a result I had to start up a second pilot, rank him up, shoot down the boss, shoot him down in big boss mode and finally get my achievement.
The easy solution I found is this. After shooting the big boss down in the arena and you land and save, copy your save to a memory card. If then it doesn't unlock the achievement you can copy the save back to your HDD and repeat the mission without having to rank up another pilot.
Gamerdad of 3
My xbox can blog