I have heard (I am not saying that this is true) - that mail in and early ballots are only counted if the votes on election day does not have a clear winner. For instance, if there are 20,000 voters and 2,000 mail in ballots - if the winner of a given race is more than the number of mail in ballots...why count the mail in ballots? (but for local races that could then in turn also be subject to the same parameters).
Then there is things like this...
Postal Office Worker Bragging About It, Claims He Uses His Job To Rip Up Trump Ballots | Conservative Daily Post