Since we only get bound to the instance if we kill the the Chief Uruk’Ar boss, i tryed to cover all the instance using track on my ranger at several spots, leave the instance and enter again without killing any mob. Each time i did this the instace had reseted. I did this about 15 times on normal instance and the boss has never spawnned. I tryed also on epic instance about 10 times without any success.
Then i thought that only one boss could be active each moment and if the boss was up outside he would not spawn inside.
So i did the same thing (use track, leave and enter again) checking if the boss was up outside before entering again.
I did this about 15 times and i havent got the boss.
I'm running out of ideas to get the boss.
although, Everytime i checked if the boss was outside i noticed that the place holders npcs werent there either. So, maybe this boss only spawns at a particular hour of the day because I've already seen outside those npcs and the boss many times before.
I dont want to belive that this boss has a so low probability of spawning that we have to reset or clear the instance hundreds of times to get him.