Did you refresh your PS4 up with the new 2.50 update recently, after installing Bloodborne? If so, chances are that the update is corrupting your files saved for the game.
As of recently, a host of users reported that after upgrading their PlayStation 4 consoles to version 2.50, they were forced to re-download Bloodborne's Day One update again for reasons that are currently unknown.
On performing the process, the update corrupted users' saved files, preventing them from continuing with their previous games. In fact, any attempt to hit "continue" or "load game" would result in a pop-up message saying that an update was in progress and that the game was unable to load. And since there's no update in progress, users came to the understanding that they had lost their saves.
Nonetheless, there's now a simple workaround that you could use to your advantage for fixing these corrupted saves: Just start up Bloodborne and start a "new game".
Once you have control over your character, head back to the main menu again and you should be able to choose "load game" and reload your original save file.
Let us know if this works for you in the comments section below. Here's a list of all the new features that has arrived with the update 2.50 for PS4.