Update: Never mind, I thought I added code that overwrote the save file if it had the wrong type in it, but I didn’t. -3e will contain an automatic fix for if you load into the menu with a broken achievement save.
For now, if you have a broken save, either delete it and load up -3d (since this version creates the correct object when you load up the main menu), or just load up any version, click “erase save data” on that one chalkboard in the menu, and then load into a level of your choice. This should fix it.