Broken slot machines do happen, and it's been made very clear that the player does not benefit.
https://www.aol.com/2016-11-02-broken-slot-machine-dupes-wom...
https://www.foxnews.com/us/not-a-winner-oregon-woman-denied-...
However, this works both ways. If the mistake is in the favor of the player, they are obligated to pay out:
https://www.msn.com/en-us/news/us/a-slot-machine-in-las-vega...