Had the exact same issue with this fight just a few minutes ago. Wiped on the first attempt (yay for first timers in hard modes...), and then when we came back in, we were unable to do any damage to the healers. I had originally thought it was because I had used cloaking screen after everyone else had died on our first attempt, but it sounds like others are having it even after a full wipe. Guess I'll be putting in a ticket as I'm sure these posts won't be considered as a ticket.