Black Barya disappeared after invul stage

Bug Report ID: #3,936,218,282

Was attacking the Black Barya and once he hit the threshold, he disappeared. The things on the side were not shooting at me. He never did the black circle attack, I did see the small towers in center but they disappeared once I went back in. Map still says 1 monster remaining but he is not there.

Can I get my item back?

https://imgur.com/a/yRtSTRu


e/ Went back to character select and back into area. Still did not pop up, so must be an instance issue.