In 1988, a presidential election happened in Mexico,

In the middle of the night, voting counts stopped. The favorite candidate had a nice gap and everyone thought his victory was inevitable. When the counts were started again, the favorite was losing bigly.

Such an event is now known as the breakdown of the system

Both political parties agreed to destroy any evidence of fraud. The favorite candidate had no way to contest the results because he had no support from his party!

A 2019 study in the American Political Science Review found "evidence of blatant alterations" in approximately one third of the tallies in the election

https://en.m.wikipedia.org/wiki/1988_Mexican_general_election