In my country there is usually a recount in some "suspicious" voting stations. The recount about never gives the same results as the original count. People are not very good at counting even if they have good intentions.

>>First grade math skills are enough to understand it: we just count the votes in every precinct, and sum up the votes later up. No hashes, no smart group theory schemes, nothing complex.

-people are bad at counting

-some people might be bad at counting on purpose

-some people might try to influence the results

This happens all the time as proven by multiple recounts. I am not talking about USA here but about EU countries but I imagine it's the same in USA. You just hope those swings are small enough to not influence the end results. I am sure this is usually true but sometimes it's close and then the odds are at least some of those elections went the wrong way.