Hm. You did it right the first time. You should ONLY give maps to adventurers who get the ditzy potion, and any maps you give to adventurers who DON’T get the ditzy potion will count against the “correct” maps given, and send smart adventurers to the mimic, beat up the mimic, and cause the game over. So I need to dig around and find out what circumstance results in a failure even though you presumably gave maps to the correct people.
The monster report IS random (usually), so any time they’re about to fight a zombie, you shouldn’t give them the ditzy potion. In retrospect, this is a slim chance that a person might get a day where they encounter nothing but zombies, and so you never give ditzy potions, and are kind of funneled into failing the mimic by dumb bad luck. Slim, but I will need to rectify that.