Ah I figured this one out -- games that use `localStorage`, a native Browser-based method of keeping track of game data -- can't access it for folks who are not logged in to itch.io. For example, if you try to play a game that uses `localStorage` in Incognito mode, you'll get localstorage errors in the console.
In the most recent update yesterday, I've omitted localstorage access completely so that anyone can play Existence Simulator regardless of logged in status.