If you opened the game after the update to discover your save data gone in slot 1, don't worry! The game was accidentally saving into a folder called 'progress1' instead of 'progress'. If you have made any progress since this update, you'll need to copy it over from that folder.
Your old data should be back (as we are now reading from the correct folder).
Changelog
FIXED - Save slot 1 was accessing the wrong file location (any lost data should be back).