It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

I'm playing in hard mode - so I don't know if that affects anything, but I've noticed that none of the special 'prime' or 'superb' guns are appearing in my game.

The chests where they are supposed to appear are either empty or simply not there.