Did you get any further with this? I encountered something similar
, though slightly different.
I emailed the developer, response from them is below:
"I think I've identified what caused this - a save file was unintentionally left in the previous Mac version, but removed from the current version. This means that the updater will have deleted your save, believing it to no longer be a necessary file. Unfortunately, there's no way to recover your exact save, but if you let me know roughly what part of the game you were up to, and which difficulty you were playing on, I can send you a replacement save file, which will get you roughly back to where you were.
Rest assured that this was a one-time issue due to a process which should have been automated, but wasn't in this instance, and it won't happen again."