Achievements don't work

[MeaGaudia]

So, my friend and I were playing the game. We tried to do the arena, we finished one and didn't get the achievement for it. Well, we thought that was weird. That's why we started clap-trap's DLC, killed General Knoxx and didn't get the achievement for that again.
Does anyone know what's the problem here? Maybe someone has the same problem?

[pulse10]

i am problems achieve knoxx-trap

[MeaGaudia]

nah, it's fine now. You get the achievements after you kill the bosses for the second time. But we definetely had troubles with arena achievements. I don't know if it's broken

[𝘽૯ṛᶰ𝔦૯35LoMaX]

http://borderlands.wikia.com/wiki/Big_Tournament That gives you the 3 achevements which you dont have. http://borderlands.wikia.com/wiki/Small_Tournament that you have unlocked