So I was in TES last night playing my Rdruid and when we got to Sha of Fear, I was unable to place efflorescence on the ground in the bosses play space. Same with the warriors in my group, they were unable to use leap, and monks were unable to put down their statues. It seems to be a bug with the pathing, which has been an issue since release.
You CAN place statues, efflo, etc, BEFORE pulling the boss and on the side platforms that you get sent to, but as soon as the light barrier comes up after the boss is pulled, you cannot use any of these abilities during the fight.
Obviously being unable to cast your statue as a monk, or your main healing spell as a druid is pretty bad.