Boss FIght Citadelle des Morts Bugged

[crisv1112]

In CItadelle des Morts, after spending 2 hours on the Easter Egg and finally setting up for The Guardian Boss Fight at the end me and a friend got The Guardian to a quarter of its life and whenever it is supposed to go immune and spawn zombies for us to survive, it just stood there doing nothing, we cant kill it, use gubblegums or do anything, so it softlocked us out, we had all perks and weapons at level 3, we had everything done right for us to win and because of a bug we are not able to win? anyone that could help or anything