Had no problem on my tank spec 37 Jugg. You can use choke, backhand and push for every other interrupt since the actual interrupt skill will be on cooldown when he starts casting again. Tell Quinn to use his freeze skill to interrupt if everything else is down and by the time that's over, your rotation should be up again.

I had the same issue. I sent in a ticket about it and the Mod told me to stay in the room and just wait about 4 minutes for him to spawn. He showed up after a few minutes and the quest worked normally after.