Same issue can’t find a fix going crazy
Yeah this is still dookey. Had to drop quest and start from scratch - poor effort Blizz
(confirmed for me) Just kill the elite adds Zayhad is fighting (all of them) and the NPC will come down allowing the quest to continue
Still happened to me today, nothing worked to damage/aggro them. Currently restarting the quest
happened to me today! so frustrating…I don’t even see a way to restart the quest.
Took a couple different tries. Finally worked when I aggroed mob packs right up against the wall they’re stuck in. Eventually they came out and were able to be killed
So what I learned after restarting the quest is if you don’t go to him first the mobs will more than likely use their knockback which knocks him into the wall. I seen that after I redid the quest and chose to go to him first. I got the mobs off of him and kept them off so they would stop knocking him back. He did get knocked back a little but it knocked him into the tree instead. Hope this helps.
i had this happen to me today, he was behind this shield wall so i got as close as i could get dropped down wild spirits and was able to attack one at a time till all were dead than he came out.
Had this happen to me, what worked for me (Fire Mage) was to drag an enemy over and use Phoenix Flames to hit the enemies out of LoS, that triggered my companions to attack them and kill them.
Can confirm, Wild Spirits works 
Lucky
not for me
still bugged in March