I've been playing since the inital launch - with that said, I know achievements were getting reset and things like that the first couple of days. Most of them I was able to redo, but some won't re-trigger. These include the Beastmaster achievement for Act I [I can't get the "new lore" to pop up no matter how many times I encounter the mob].
In addition, some of the conversation achievements are not attainable for me [lvl 60 Wizard] despite how many times I talk to all the different NPCs [Leah, the followers, Tyreal, etc] to continue their storyline. I'm not sure if it's because I'm missing some trigger - I was able to complete a couple parts joining a friend's co-op game, which makes me believe my hero is breaking and/or bugging out the requirements to see these conversations.