I have reported this bug a number of times as it occurred almost half a decade ago. It happened back when T6 was at the top of the list lol.
I have an entire achievement tab that cannot be marked as 100% completed because a lower tier of an achievement will not finish. The highest tier of that achievement is already done. I continue to get the run around by the developers and the help desk folks. My computer has been updated/replaced many many times since and I have installed/re-installed Diablo 3 on other PCs to check this directly. So I can confirm with 100% certainty that this is within my account itself and not part of the local cache.
Career Tab > Adventure Mode > Nephalem Rifts > Death, Death and More Death (cannot be completed)
Some Hordes = complete.
I have no idea why no one will take ownership of this issue as a quick search of the forums shows a few other folks running into this and even in the last few months. I have screenshots and a decently memory from when this happened so please do follow up with me for this.
Edit:
- Just Riffing: 3/29/2014
- Riftual Sacrifice: 4/16/2014
- Monster Mangler: 5/24/2014
- Dedicated To Destruction: 6/6/2014
- Bad Time To Be A Beast: 2/14/2015
- Killin’ It: 7/14/2015
- Death, Death and More Death:
- Some Hordes: 1/9/2016
Some additional data, the dates of this tier of achievements.
I am unsure of the exact mechanics of this achievement in that I do not know if each tier requires the entire count, or simply the additional value to reach the next goal, as a result, my theory is lacking. But it seems like between 6 and 8, it took considerably longer to reach the goal. I suspect that when 7 triggered it instead reset my counter to 0 and did not mark itself complete because it couldn’t properly evaluate my count.
However if instead this mechanic is more along the lines of triggering the achievement and then zeroing the counter. I would suspect that for 7 it possibly tiggered in the incorrect order, zeroing before marking complete.
Unfortunately I have no way of knowing when 7 triggered itself. Due to this I cannot pinpoint any possible causes. I would suspect replicating this under controlled conditions would be near impossible. I do suspect I was playing on a WD at the time, likely with a pet build. Again, long time ago so hard to say.
Correcting this part would also require one or two additional things. The achievements themselves should have an additional trigger that follows the logic, if the greater tier is marked complete, mark complete. Short of something like that or some form of a check on the account metadata for everyone it seems unlikely this will ever be resolved.
Or you could simply give the support team a way to reset these tiers for everyone who comes along with this, and I am sure most will be more than happy to just complete whatever objective it is that screwed up. Not having the ability to do this for us is shocking.