Some things are silent, but deadly and Metal Gear Solid V: The Phantom Pain's Quiet is one of those things. She's so deadly in fact, that bringing her along in certain missions can corrupt your game and cause you to lose all your progress.
Bringing Quiet along as a buddy in either Mission 29 or Mission 42 can create a game loop that will ultimately corrupt your game – as you won't be able to escape it. Apparently, the loop begins and a loading screen… then never leaves the loading screen because all it wants to do is reload that screen over and over!
The simple way around this is to leave Quiet behind for both of those missions, just Fulton her away.
The developers are currently investigating the cause for the bug and once they know what the issue is, they will be resolving it. Last week, Konami limited online services, then shut down the online servers entirely (they turned them back on shortly) to get the online features up and running – you can tell they are working overtime to get the gameplay experience as smooth as possible.