[Edit: TL;DR: found a workaround.
Issue: the game stops autosaving on Iron Mutant (CE-30028-3 error) when playing the Seed of Evil DLC, and locks you out of the Tough Nut trophy.
Workaround: to get back the autosave routine, fiddle a little bit with your team roster and fast travel to another zone. If you still get the error, try again… ]
Bug occurred twice on PS4 Pro, once on vanilla PS4 with the physical edition. Both fully up to date, as well as the game.
Played the game + DLC in normal mode without a problem. Then went on with a Very Hard/Iron Mutant run, finished the original campaign with no trouble (got my shiny trophies) then started the DLC.
I was doing quite fine until the first side mission, where I got a CE-30028-3 error (“an error has occurred”), plus an in game notification where the floppy logo should have been saying “failed saving out of disc space” [needless to say, I have more than enough space]. Tried restarting, restoring a cloud save, nothing worked, the game kept on giving me this error and deleting the autosave. I decided to rush the end game (no point anymore in grooming my characters for an hypothetical future DLC), with no save, but thinking it was Iron Mutant after all. Finished the game and got no trophy.
I deleted everything (game, saves), rebuilt the database and reinstalled the game. I tried my cloud save but got the same error.
So I started a totally new game, playing DLC only with stock characters on Iron Mutant, and everything was fine until the very last fight! I was almost done and the error occurred again! I still decided to finish, of course, but didn’t get any trophy, so it must be tied to the actual existence of the autosave.
Lastly, I picked my original PS4 off its shelf, installed the game and tried my backup. Same “crash” after the same number of autosaves, whatever the actions or what induces saving (whether it’s fighting, travelling, etc.). Will try a last run from scratch where I’ll be seriously under leveled and badly equipped, just doing the bare minimum to limit the saving, but I’m starting to have a bad feeling about this one.
I found a thread here on the Funcom forums (can’t post a link, but it’s called “failed-saving-out-of-disc-space/49917”), seems it’s a problem some PS4 users have had since the beginning.