Tried the Ropalolyst fight again. New discoveries: In a two person squad, we were able to kill the Ropalolyst with no issues. In a four person squad, Ropalolyst turned invincible at the final stage (again) and kept teleporting away from the moon shot. New observation - the Ropalolyst acted as if one of its synovia regenerated (appeared as destroyed visually), and the empty space where the synovia was would take damage too. We couldn't destroy the "regenerated synovia" so we all had to abort the mission.
Same issue here for me yesterday and today, in the final stage of the fight the Ropalolyst would go invincible (grey health bar) and not take damage. If we tried to use the moonshot laser on it, it'd insta-teleport away and nothing we did in our frames or Operators could hurt it. It'd show damage numbers if we hit it, but otherwise just fly around, scream, and regen its "health" in its grey health bar.