Bug Titan Grotto boss act 2 cruel

So I was in a party this morning, and I noticed that for a min or so I could not do dmg to the boss. I spammed AOE, went to single target skill, everything I tried did not work. Me and party member was taking dmg but could not do dmg to the boss. I was on ps5 I don’t know about my party member though. No lag or anything. Could have of been a 10 second fight turned into a 5 min fight.