This achievement just doesn't seem to get awarded, no matter how high of a mighty blow call out I get. It doesn't even seem dependent on which monsters are killed.
What do I have to do to get this achievement?
Even though the known bugs list was updated, this issue has yet to be included.
There are thousands of bugs in our database. The known issues list is not a comprehensive list of all issues that are known to us. Having said that, there have been multiple bugs on this achievement in the past, all of which have been fixed and thoroughly tested. We have not been able to reproduce any problems at all with this achievement internally. There have been sporadic reports of people not receiving achievements that may have been earned just prior to a maintenance period or patch push, so it's possible it's related to that. From my end, all I can really do here is verify that the achievement works in game as intended, which it does.
You can try contacting customer service to get an individualized report and have someone possibly take a look at your account in particular to see if there's anything that can be done to correct your achievement status.
It seems they fixed the issue, I just got mine yesterday as well, Thank you Blizzard.
Yes we pushed the fix for this during Tuesday maintenance. Everyone should be able to get this achievement without any issues now.