Achievements Question/Issue

The catalyst for this post is that I have apparently not acquired the Zombie Horde achievement. I play a summoner witch and currently can summon 10 zombies and 11 skeletons (I realize the skele's don't count.)

Are some achievements PC only or something? I'm now wondering if there are others I've "completed" but not gotten credit for.

TIA :)

Hmm says summon 9 Zombies?

Maybe a bug as we normally run around with 10 (though I'm using 5 in my current build) and it hasn't marked off in my achieves either.