Ciergan at Foundry map is bugged

After killing the boss, it's metamorph is still alive and it's glitching out.
It's appearing and disappearing, while attacking.
Where seemingly nothing is happening on the map, something can out of nowhere use some skill that bypasses shield and eats 4,500hp on one hit.

That attack looked like something grew and popped beneath my character, despite being on the move, it still one hit me.
Can I get my exp back?