Yeah I have the same problem on Xbox 360, but it's 2 achvments on mine.
So I've unlocked all 16, yet only shows 14/16.
(To Chakie, at any point of Episode 2, did u have to replay any part of it because yr game save f*cked up?. I did, after the barn section. So I think it's the 2 achvments I unlocked in that section, before I had to replay it again (that was an hour wasted which I'm never getting back lol). I'm thinking the glitch had something to do with that maybe?