As far as i know they fixed the boss on the last patch, by adding an "enrage timer" which spawns extra elites when the time you had to complete the puzzle runs out. Also, the mobs don't spawn when you click the keypads they keep spawning untill you complete the puzzle, so you just have to manage and solve it the fastest way possible and for that you need to know the order of the colors if you click the right or left keypad. If you use the right keypad the rotation is as follows: Blue, Green, Red, Purple, White, Yellow If you use the left keypad the rotation is as follows: Yellow, White, Purple, Red, Green, Blue It is advised that it is always the same person clicking the keypads in order to not mess up the order. If you are doing everything correctly and still bugging for you, I found on this website http://starwarswarrior.wordpress.com/2012/01/12/eternity-vault-guide-ancient-pylons-8man-hardmode/ that in order to avoid bugs you should complete the several lines of the puzzle in this specific order: North must solve the 1st Symbol first. South must solve the 2nd Symbol first. South must solve the 3rd Symbol first. North must solve the 4th Symbol first. Hope this helped solving your issues with this boss. Cheers

Nice stream