Thanks for reporting this, that’s a really helpful catch.
You’re right — this is a browser-specific issue. On the web version, progress is currently saved only when the game explicitly triggers a save (for example via the save option in the settings menu or when the player leaves the game view properly).
That said, the flashing / zoomed screen is definitely not intended and counts as a real bug.
Thanks again for taking the time to report it — it really helps improve the game.