I played a new game and worked my way up to All-star without an issue, so that leads me to believe that this might be an issue with the game files themselves. Either through mixing different versions of the game, the files being edited, or perhaps an issue with migrating the old All-star scoring/tagging system to the new one.
Could you try downloading a new build of the game, keeping it separate from your old build by putting it in its old folder, and then see if the issue persists? Your save file is saved outside of the game folder, so you should be able to play All-star mode again right away.
Other than that, I think the best thing I can ask for is a copy of your save file. I'm not sure if Itch.io will be happy with you trying to share a file or a link to download a file, so send it to my support email: hornymelondev@gmail.com
The save file should be located in this path, depending on your OS.
Windows: C:\Users\<username>\AppData\Local\HornyMelon\
Linux: ~/.config/HornyMelon/KeinesExpandingClass/save.json
Thank you for your patience and I apologize for the trouble!