Konami might have fixed the MGS 5 Quiet save bug but now there's a new one that only affects PS4.
The issue arises if you have multiple PSN accounts on your console. If that's not you then walk away and stop worrying. Everything fine, life is great. Appreciate what you have.
If you do have multiple accounts though then be wary. Apparently there's an issue that could trigger this message when trying to resume a game: "This saved data cannot be used, as the relevant downloadable content cannot be found". If that happens then it's impossible to start playing again.
Konami is "working on methods solve this issue", but for the time being say you should only play the game with a single account logged in.
Here's the full message:
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