Konami is working on a Metal Gear Solid 5: The Phantom Pain save bug which occurs when bringing Quiet along with you during certain missions.
According to the developer, if you take Quiet along on Mission 29 or 42, the save will become corrupt.
The only way to keep this from happening is to not bring her along on these missions.
This affects The Phantom Pain on all formats. We'll update this post with more information when it becomes available.