Cuachic Vault boss fight bug

I just had a really odd bug happen to me in the Cuachic Vault boss fight.

I somehow managed to only spawn 1 of the 2 people in the arena while the other just kept sitting on the platform they originally sit at before the fight starts.

He seems to technically still be in the fight as he will throw spells at me when I work close and his HP bar appears at times.

Heres a verification code from the instance: 7jch48dt3c9z

It was possible for me to make him jump off the platform after hitting him with some projectiles from an odd position. So he isn't permanently stuck there.

Also please ignore the 2 extra bars below my character, those are just frame clones of my block / rage bars.