Yeah, this happened to me too on my first ever run (I've bought the 30th anniversary today). I managed to reached to the final boss encounter on my own and everything you said here happened to me too. I must add that, with some help of two friends in order to not restart the entire encounter all over again, when the damage phase starts, Avarokk is still immune to all damage and the damage phase is infinite (the growing crystal won't shrink to its initial state). In other words, the dungeon is atm impossible to complete and those within the first steps of the Ghallarhorn exotic quest, like myself, won't be able to complete it untill it's fixed.

Same issue here. Will add details and observations of my own. (Made with the help of a friend) The final boss encounter faces multiple issues. Experimented results are the following: >Boss does not move, shoot, or stagger. Sometimes will look around here or there. Does not appear to stagger or move from original teleported location from beginning of the boss encounter. Stasis and Missile titan supers seem to not be able to cause staggering, either. (possibly due to immunity.) >Engrams/motes spawn in the spawn boxes upon mechanic interaction as intended, but are not released from the boxes (usually). The boxes do not execute their drop animations or functions related, otherwise. - Sometimes, engrams do drop if the box spawning them continuously keeps spawning them from continuing to shoot the engram mechanic until one or more clips through the box and falls. >Not sure if this is intended or not, but the "shoot this with a scorch cannon" objects all remain open the entire time regardless of interactions. >Upon successful crystal filling, the boss does not exit it's immune state. No change. >Damage phase does not cycle in observable behavior. (No visible changes pertaining to crystal filling. Does not reset after an amount of time.) >Boss may not do anything for the most part, but the only visible reaction he seems to have is stomping occasionally when the player is in proximity. ---- Hope this helps. (I see much of this already is covered if not all of it.) ----