If you’ve recently fallen foul to the achievement bug whereby you aren’t being rewarded for some of the achievements you are, um, achieving Blizzard have rolled out a backend fix that should hopefully remedy the situation.
Without going too deep into the technical details, basically what we did was implement a system that looks at your account upon login to try and identify any achievements for which you have fulfilled all the criteria, but have not been awarded the actual achievement. If the system identifies a broken achievement, the server will attempt to immediately ‘heal’ your broken achievement and grant it to you. I say ‘try’ because each server will only attempt to run a certain number of instances of this healing operation at one time. What this means is it may take several logins to heal any achievements that are broken on your account in this way. This is expected behavior, and just because you haven’t seen any changes to your achievements just yet, doesn’t mean that the fix did not work for you at all.
I know that many of you have been waiting for this for a long time, but it is somewhat likely that this fix may not resolve every single achievement issue that every player has. This particular fix is specifically targeted at achievements with tracked criteria (basically this means requirements that were tracked with checkboxes). Also as I said above, this fix may not take effect for everyone immediately. What this means is that we are going to need to let the dust settle over the next few days to see what other types of issues remain.
So, where do we go from here? At this point, we encourage you to simply play as you normally would for the next several days and see what happens with your achievements. If you are still experiencing erroneous behavior or are missing a particular achievement that you believe is broken, we encourage you to reply to this thread and let us know about it. Include detailed information if you can such as the full achievement name, when you earned it, and what the exact problem with it is with as thorough a description as possible. Steps are good too, if you have them!
TLDR – Fix has been applied. Logging in should update your achievements but if it doesn’t, keep trying. Play as normal and if after a few days it doesn’t fix then post in the achievement bug thread.