We did it 2 times with a full party for the raid and both of the times the giant guy became stuck without moving anymore.
anyone experienced that before ?
edit now: after some thoughts... i belive that the giant react to some epic feature of someone of the party... since the first time we try it at some point (when everyone but me decided to leave the raid) he restarted to move and fight.
i am lvl 20 but the party was full of epic toons, so i belive that is something related to epic features (i have no other clue atm).