Same, I had to do an extra run as well. After doing some research, I found out that it can happen if you kill the first boss too quicky. Not sure what "too quickly" was, so I made sure to just whittle him down on his last health bar. I also read that you might be able to get the softlocked boss down if you can manage to push him off/get him to follow you off (I was unsuccessful with either). I'm loving my Barrow-Dyad and would say the extra run is worth it. After the Derealize Conquest, I ran the rest on Grandmaster difficulty with only positive modifiers. Keeps revives after the timer ends. I'm free most of today and tomorrow, if you want help.