Thanks for letting us know. I'll look into this and update the achievements soon.
Update: I've updated the achievements now. There was a rogue DLC pack attached to some of the achievements causing them to show an "Unknown" rarity level. There are checks in place to ensure that doesn't happen again.
Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete.
Otherwise, please post a new thread in this forum instead.