In order to unlock all the achievements without any problems, you need to fulfil some conditions:
Firstly, you can play the game offline and, as soon as your console connects to the Internet, it will synchronise the save data automatically and update the achievements. We suggest that you have your Xbox Live® / PlayStation®Network / Steam account connected when playing the game.
Secondly, make sure to complete the mission and reach the Reward Screen, after the cut scenes and end credits. Please do not skip this part by going back to the Main Menu straight away as it is only after the Reward Screen and by being connected online that you will be granted your achievements.
If several achievements are supposed to be unlocked at the same time but don't pop up, please try to re-trigger the non granted achievement condition again.
Try your best to unlock all the achievements and challenges to reach the 100% completed game!