My friend and I just got flawless raider while two manning normal Crota, and the achievement hasn't unlocked. I'm on Xbox One and it's normal for achievements to not unlock right away. I normally restart the game and it unlocks. However, after both of us restarted our game, we still didn't unlock it. We even waited for about two minutes after we completed the raid before returning to orbit. If you don't believe me, just check my history. Help:(
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According to the Xbox Support page, a way to unlock your achievement is to restart your console by going to; Settings > Power and Startup > Restart Now Select the option to restart it when prompted. However. The page also states that it can take upto 72 hours for achievements to fully unlock as your profile synchronises to the Xbox live servers. This worked for me recently with 15 World of Tanks achievements that weren't unlocking.