I've updated the game to v0.25 - it comes with a more robust auto saving feature that autosaves every 60 seconds. However on web this is still limited to saving progress via cookies, and there is a limited amount of file size the game can store at once.

Additionally, if browser cookies or temporary files get deleted, progress will still be lost, in which case I recommend trying out the desktop version as it comes with multiple autosave slots that will prevent complete wipeouts!