The sneaking sniping has to go. I had Lae'zel, Astarion, and Shadowheart trigger the Bullette fight. Game glitched and my MC didn't go with them.

So, I snuck up with my sorcerer and just endlessly pegged the Bullette with Firebolt until it dies. My companions kept him in frozen combat status while I just slowly dwindled him down and killed him.

When one member triggers combat, everyone needs to enter combat.