Did you switch ren'py versions? Many of the games I've played have either broken or wiped out saves when upgrading ren'py.
Viewing post in Important notice/old saves not working comments
Initially? Nope. I was on same version. However, for some reasons it kept breaking. Sometimes of first load it would work, on second the same file would be corrupted. There was quite a lot of script changes, however something broke that shouldn't so I decided to call it early and move on, rather than work for it for days, possibly without fixing it.
I did now download new Renpy though, I've been on older version.