The achievement “Pest Control” (involves killing critters across Azeroth) has a bug regarding how it tracks progress for completion. Normally, an achievement like this is able to be completed on individual characters with individual tracking of progress (because it’s NOT an account-wide achievement). However, despite the progress tracker telling me I’ve killed all of the critters on a given character (even when I haven’t killed those critters), I still can’t get the achievement on that character.
UPDATE: I was able to get the achievement despite the tracker being bugged. Please ignore.