"S" is the key for checking sanity, not 5. I can see how some confusion may come up with the small pixel font, I'll look into making it clearer in an update!
Should be fixed up now, there was an issue in the save script about where a variable was saved. Now it should work fine from a new save file and you can use S or 5 to open the sanity menu to hopefully stop any future players getting mixed up!
