Never seen this before in my life, not sure if it pertains to heroic only or normal as well, but basically the following was happening.
On entering the instance random members would not have portals to the maelstrom. The portal at the front would lead to gunship (which would then have no portals on it) - If you wiped and went in again, different members would have this issue. (jumping off gunship and dying may or may not resolve it for you.) Ended up getting through it by just using many mass resses and summons, but was really annoying with no warlock around.
Any ideas on how to stop this in future? :P