Corruption boss disappeared after dying

Bug Report ID: #1874169980

Killed all rares. Killed the normal map boss last. The corruption boss appeared. Died. All monsters are gone (0 Monsters remaining) and the game tells me to kill the normal boss. Which i already did and is not present.

Side note: Having the corruption boss spawn after the normal boss without the possibility to heal or to get flask charges seems a bit harsh that early and on that low level.