One of the Treasure Hunt items reads

> 
> Chapter 15: Destroy 8 of the Aurum Core's guns
> 
> 
> 

I just finished the boss fight on intensity 6.0 and there were only six guns. I blew them up right away and waited a few minutes, but more didn't appear. I also triggered the second stage of the boss, when it starts flashing red, but none reappeared then either.

How do I destroy eight guns?