Hi!
In July we changed the names of all the characters in the game and Ren'Py really didn't like that.
Basically, since Ren'Py stores everything using character names, it causes issues with save files — save file has an old name, and the game no longer has that variable.
So our programmer tried his best to do a migration system that would take care of that problem, but it's not perfect, and sometimes the save file gets corrupted.
That's what probably happened in your case and we're really sorry for this :c
You can try using "Skip to new content" option at the start of the game or use a Gallery unlock in the settings.
Again, sorry for this, we're working on our save system, but it is taking A LOT of time and a fix/solution will be probably pushed out with the Overhaul Update later this year.