MGS V: The Phantom Pain Deleting Save Files

Konami have posted, via the game's official Twitter page, that there are certain conditions that will result in a deleted save file.

Until updated; please avoid playing missions 29 & 42 while using Quiet as your buddy, as this seems tied to the cause of the issue

— METAL GEAR OFFICIAL (@metalgear_en) September 8, 2015

People have, understandably, asked for some clarifications. Such as which formats are affected:

@StephenDullin this issue affects all platforms

— METAL GEAR OFFICIAL (@metalgear_en) September 8, 2015

There are also multiple tweets stating that, if you have completed both 29 and 42 with Quiet without issue, replaying the stages may still cause deletion!

They are working on a patch, but until it hits, avoid using Quiet for the 29th and 42nd missions -- or play it safe and avoid using her altogether.