Originally Posted by NeedleGames
Yeah, sorry. After posting this it asked for my login details again and now it's working. That still shouldn't have happened.
Your login session can be expired for various security related reasons. Such as a changed password.
I'd have to check in with the backend guys to check to see if something happened at a larger scale to log users out, but it could also happen if your app data was corrupted or wiped and your access token was modified in the app.