So, I saved my project through Cloud, service Google Drive, exactly the same as I normally do. I can open all my other projects fine. However, when I came back to this project after a short break, it says that it isn't a valid Construct 3 file, but is still a .c3p. I'm on the proper C3 version, r309, and it won't work. I spent a lot of time on this project, so if you have any suggestions please comment.