Black Crow Blooming Field - no phase transition

Entered a T15 Blooming Field map with the Black Crow boss fight. It jumps down from its pole and the fight begins. In a couple of seconds i have it down enough for it to enter it's second phase. However it never moves to the second area where it usually gets the bell. Instead it "grows bigger" in the first area and then just keeps attacking me. At this point i can bring it down to half the health but after that it will no longer take damage.

I had 2 revives so i let it kill me once and when i respawned at the checkpoint and went into the fight again, the same thing happened once more.

Baiting it into the second area or back into the first doesn't seem to affect the outcome. The door back to the rest of the map obviously never opens either (only on respawn)

edit: second respawn and it's the same issue. I don't know if it's helpful but the Witches' voice line is triggered (something like "don't run, we're just playing"). The Crow just never leaves to the next area

Happened to me just now. Same map. Got him to where he should go to phase 2 and he just become invulnerable and no longer reacts to hits. This was in T12 Blooming Field. Even after respawning.