That's odd. You may wanna repost this in Technical Support to get the team's attention.

It makes me wonder if it's some kind of physical issue with the PS4 HDD itself, though you've mentioned it's only XIV, so I'm not sure. I haven't seen any report of this before, so for now it seems to be an isolated issue. Did you try deleting the XIV app itself and not just the save file? I'd wipe everything from the PS4 regarding XIV and then give it a try. Hope you can find a solution soon.