Hi there! Sorry for the trouble. I think it has something to do with a version of Ren'py that did not mesh well with the Steam Achievement Libraries. We tried a lot of fixes but couldn't get it to work. It was out of our control for a while.
Fortunately, the recent update on Ren'py fixed this bug, and we're working on an update right now. Hang on tight. A new version with working achievements is coming!