Blizzard does not allow GMs to award achievements. If an achievement is bugged, the first step is to check it on Wowhead then try to repeat it. If that does not work, they can put in a bug report. That will NOT give them the individual award though.
To get the reward they are going to have to wait for the Devs to fix the achievement then probably repeat it.
There are RARE exceptions to this, but generally not. The GMs are not allowed to touch achievements.
Game Masters are not able to resolve potential bugs in-game, though they are sometimes able to help with issues caused by a bug.