It seems like you can't create matchmake-able sessions of the Zariman void flood/cascade and Sanctum survival/alchemy omnia fissures from the orbiter. If you start one from the orbiter, no one seems to ever join your session.
BUT, if you start a fissure from the mission rooms in their hubs, people seem to be able to join your session from their orbiters.
Also, enemy levels in the steel path versions of these are +100 over listed; i.e., I did a Murmur survival listed at level 163-165, and enemies started out at 263.