Act 3 Boss Queen can become invulnerable

During the boss fight we are surrounded with all the Royal Guard that cannot be killed / moved through in any way .

At some point the Boss Queen start levitate / jumping around and it happened to me she ended behind the guards : making her impossible to be targeted and also damage me in any way .

Had to respawn to redo the fight .

This also happened to me. Restarting the game didn't help. I had to die/respawn to reset the fight.