Hallowed Ground Maker of Mires Bug

I killed all 4 of the other bosses in a T7 Hallowed Ground map. Now the main boss (Maker of Mires) is the only one left, and he's supposed to be killable now, right? But I still can't damage him at all.

I think one of the bosses glitched, because it still plays the intense music when I go to where I killed it. I've been standing around and running around all the edges in that area for a while just in case it was hiding under the cliff or something, but it seems like there's nothing else I can do. I see its corpse here.

I ran around the entire map again just to make sure there were no other enemies I missed. But nope, the main boss (Maker of Mires) is the only enemy left on the map. Still can't touch him.

NOTE: if it helps, I killed everything super fast with chaos damage over time (Toxic Rain). Maybe the boss death trigger got missed because of all the fast stacked DoT's everywhere?

Bug report reference # 1,006,224,129