Hey I actually had a similar bug to this where during Solidago's Boss fight it happened on his final hitpoint. It caused his defeat dialog sequence to loop twice, and then I didn't get the proceeding cutscene where the screen shakes and you're directed towards the mountain gate. I don't know if it's game breaking because I reset instead of trying to find out, but figured I should bring it up regardless. I've been recording my playthrough for the video I've been working on so I actually have footage of it happening, which you can see here:
Hope this helps, love the game!