Lephantis Phase 2 Not Spawning

[Recaiden]

Observed 2 times as Client in a 2-palyer Derelict assassinate.

After killing the 3 heads, we would both fall into the lower arena.  I was stuck in place for a few seconds; no cutscene played.  Once I was able to move, there was no boss to fight (for me as a client only).  Lehapntis's model spawned in the center of the room, with all 3 heads overlapping, but it had no collision and did not move.  No smaller Infested spawned.  My sentinel continued firing at some unseen target.

The host player was able to see and solo Lephantis.  We were able to revive each other when downed by the lightning pools.  After killing Lephantis, they were able to go to extraction, but for me, the barriers over the doors remained.