After completing the main quest in torchlight (after level 34 of the mine), the player can continue in another dungeon. I'm well past level 60 in that second dungeon, but I never got the "Deep Delver" achievement for reaching the 50th floor of a dungeon. I checked the progress, and it shows 34/50 – as though the achievement hasn't been acknowledging my progress through the new dungeon. I noticed the same for the "True Delver" achievement – it's stuck on 34/100. Any thoughts?
Update
For the record, I ended up getting past this. It turns out Torchlight was keeping track of my dungeon level, but the steam achievement progress bar needed to be manually refreshed. In addition to this, I noticed a few things about achievements in torchlight. First, almost all achievements only update their progress when loading a level – so if you've been sitting in one spot selling items, smashing barrels, or fishing, and the progress counter isn't updating, don't fret – simply walk through a portal and when you get to the other side, you should be able to refresh the achievements and see your progress.
Best Answer
The Torchlight achievements are generally buggy. I had quite a few problems with them myself, most of the time exactly like you describe it - a counter stopped working. (In my case it was for sold items and killed trolls, if I recall correctly.)
So you're not alone (look e.g. here), and there probably isn't much you can do. :(
Edit: It just occured to me: saving achievements doesn't seem to work when you're offline. But somehow I presumed that would not be your case.