I don’t know if its just me but I do not get any dialogue from Jack whenever I fight the Warrior at the end of the story. I do get some from Lilith whenever the lava rises but none from Jack. If look in the shield thing where Jack and Lilith are, I can see Lilith motioning whenever she says something. Jack does the same thing occasionally, so it’s clear he’s supposed to be saying something.
I’ve had the same thing happen to me before too. I could see him talking, but no words came out. All I could hear was the background noise and some type of humming sound as well. I can’t recall what character or what PT it was on, but I have had that happen to me as well. Probably more than once I believe… Its jst a bug imo, sometimes it happens, sometimes it doesn’t. No biggie tho