I’m going to copy/paste what I wrote from another person’s post with the same issue:
"I have the exact issue on the first realm I made with The Breach. I reported it a few days ago here: [Progression Blocker] [Boss: Brood Fight] The Brood Fight Does Not Trigger
Since then, I started a new realm and blasted through the campaign, eventually defeating the Brood encounter without leaving the area.
I’m sure this will get patched up eventually, but you may want to consider a new realm until then."