On Stadia, the High Celebrant hunt suffers from multiple glitches that I have been unable to overcome. First, the 'residual energy' left behind in the Dreaming City is unable to be destroyed despite showing damage on my first shot. Second, if I deal too much damage to the High Celebrant in its first damage phase, it remains in the Dreaming City and becomes inert, but killing it does not progress or end the mission.
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This is on all platforms as well.