Bear in mind that I was stuck on that fight for nearly 30m, so I didn't quite get all the details.
I was having a bad run in...what I'm assuming is the final fight ||Weapon's Core||, so I tried "Restart from Checkpoint" rather than waiting for a death.
Upon restarting, I did not have full health. I stepped forward and attempted "Restart from Checkpoint" again.
This resulted in a permanently-stuck loading screen, I had to exit the game in task manager.
(Is there a log saved someplace that I can upload? I'm wondering if it's due to how the final checkpoint interacts with restarting vs character death, since "Restart from Checkpoint" normally costs a life.)