Bug Report ID: #2973559444 Map Boss "Defeat the Black Crow" on Blooming Field broken

As the title says:
The Boss does not enter his second stage and after getting down to just above 50% life, he stops beeing able to be hit. Even after I let myself get killed (loosing the rest of the map) and try it again, the same happens again.

Maybe also reference Bug Report ID 3.358.913.357 which I took inside the broken area - if that helps.