The overseer Scorched Sky ivine Intervention will not update in the achievement list making it impossible to do the following task and complete the achievement. This has been buggered for over a year now and I really had expected a fix before now. BTW it would be nice if we could retire the excess agents like Santug & Sol Ro that are not of use.
I think I figured out on these Overseer quests last year (at least the Christmas time set) that if your quest has a critical success, it won't update your achievements. Until they fix it, you could try running the quest again and hoping for a normal success.
If it still pops up in your list of available quests then just keep redoing it. I have noticed that most of these special ones have to be done 2 or 3 or even 4 times before they update properly. In other words if you still see it as a quest you can do then it hasn't been done to where it counted. Unless it already has counted and then you can still get it again .
On one of my accounts I had Divine Intervention checked in the achievements. It is now waiting for the 4th run of it to get done and it is unchecked and Plunder the Plane of Fire is done and checked. This should make a backwards check. Going to have 4 Solusek Ro's!
