I'm wondering what the exact problem is that causes this bug. Is it whether a well has been found/activated (and marked as such on the map) before?
The achievement is supposed to be you have activated the well while Azandar is the active companion. However, the check is misflagged - instead of awarding the achievement progress if Azandar is currently active, it awards it if Azandar is uncollected.
I got the check for mine well before I even unlocked him. That also means that accounts who have already unlocked Azandar on one or more of their characters are barred from this achievement until the flag is fixed.