This is probably one of the biggest problems with the latest update. Whenever the PS4 system is turned off improperly, while you are playing in one of your worlds, your world gets corrupted and you are forced to delete the world that you spent so much time and effort on. It is very sad! The only way to prevent this is to make copies of that. Nevertheless, it won't prevent you from losing hours of progress. Me and some my friends all lost world saves to this issue so I know it's not a problem with my system alone. Please fix this as soon as possible: PS4 systems turn off improperly more often than you think.