So I bugged this last night but I wanted to give a heads up as this particular instance is rather time consuming and very frustrating to do - even when the boss isn't bugged out.
I aligned all the mirrors (thankfully this wasn't my first time through this Instance - so I knew basically what to do and it only took me 30 minutes to be reminded and get all the beams of light heading the right direction - as opposed to the 2 days it took me the first time.) I destroyed the Gift and jumped down the broken webs area to where the boss is supposed to be - on the glass floor thingy)
And guess what?
I waited for a while - jumped over the edge to force defeat - and started back from the ledge - still no spawn.
I ported out and came through again - no luck - I used the function "Leave Instance" and was ported to where Broin was and started the quest again - no butter!
Finally I left the instance and canceled the quest. - Broin said I had to wait 4hrs before I give it a retry - so I bugged the instance and logged for the night.
I was just catching up on the epic story line with this toon and cant really do anything else until I kill this boss and proceed with the epic - so I am reluctant to go through the mirror alignment phase again if the boss isnt going to spawn and I cant complete the quest - I would rather log a different toon and do something else until I was reasonably sure that the boss will spawn and I can proceed.
Is it possible that I am doing something wrong? I figured if the only quest objective left is Defeat Ergoth - and I can get down to the glassy floor area by beaming the lights (4 of them all converging above the web barrier and one beam shining straight down - breaking the webs) allowing me access below - that I should be doing it right...right?
Anyways - I gonna try it again tonight unless someone knows for sure that this isnt random and that the boss wont be there till a fix is patched.