I get this error message “Failed Saving out of disc space”, despite having around 100Gb free(according to settings menu on the PS4). This started to occur later in the game. Saving worked fine before.
I just got this same error this weekend. And what’s worse, every time I try to save now it seems to remove one of my save games. So now I have no save games left and I can’t save my game due to this error. I think I’m pretty close to the end, this started happening in The Forbidden City. Hopefully this doesn’t stop me from finishing the game.
Not sure but it sounds like a similar problem that’s common on PS4 for Fallout 4 players who use Creation Club.
Might be a Cache problem or something to do with the PS4 architecture.
You could try a Reinstall Database and unplugging your PS4 when not in use.