Hi there, Here is a clip I took using Medal of the boss not spawning on Old secrets, New Challenges. The voice dialogue enters a few seconds after starting the engagement that the boss was defeated but doesn't clear the mission as he didn't spawn.

I am having the same issue. The boss with yellow bar is not spawning and ive finished defending all the platforms and cleared all the enemies. Final boss does not appear and no chest shows up on platform. Definitely needs a patch as I complete this quest.

Hi again, ran the quest several times now and boss will not spawn. Would really appreciate a patch for this as its blocking the whole exo story line

Hi, afraid I have the same issue. Afraid I’m not savy enough to upload a video of it, but its at the point where the gate lord should come through the portal. Have cleared all adds, unlocked two white boxes on left and right. Then killed three wyverns and two turrets and shot both white boxes by portal. No adds alive, all six unlocked but no boss spawn. Re-ran mission again and same result.