Hey all !
Actually, it seems that the respawn rate in the instance "Black Castle" in Khopskev is bugged.
Mobs there spawn incredibly fast. When I was 31, it was quite annoying, but at level 35 it's actually GREAT !
I've been able to farm the last two bosses for 1 hours and got a lot of Greens/XP.
By the time I kill the last bost, and come back to the previous room where the boss before the last was, it would have already respawned. You just have to kill it, clear the way to the last room again (takes around 3 minutes) and kill the last boss and so on
Enjoy while it lasts !