JS RPG tutorial Error

I recently finished the RPG tutorial and tried it out. I went to the cave then fought the slime monster without making any purchase. After a few attacks the health status changed to “NaN” rather than 0. It also allowed me to keep playing rather than bringing up the location. I looked through my code but am unable to find the error. Has anyone else found this true with their code?

I’ve tried it few times, playing with code from last step - https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures-v8/learn-basic-javascript-by-building-a-role-playing-game/step-172 - without such issue. I was going Cave → Fight slime → Town square over and over again, until health was going below 0, which ended game.

If you are able to reproduce it, could you provide the exact steps?