Having been on the inside of Canadian politics, I will admit that there is there are inconsistencies in elections.
First, voter lists are hard to maintain with 100% accuracy. Unfortunately when an administrative mistake is made, the other side likes to claim fraud.
Second, over zealous party workers (sometimes disguised as neutral polling station workers) try to tilt the balance towards their preference.
The first can be minimized with attaining a high accuracy, maybe 95% or 98%. The second can be attained with good rules for scrutineers. If the parties cannot find the committed volunteers to be scrutineers, then the blame should lie with the party.
Mail-in ballots can be a problem. So too can in-person ballots. Should we ban in-person ballots as well?
When an election is decided by administrative errors or a little cheating, the both sides were viable contenders for the elected position. But there is no way a modern election can give a candidate with 30% of the vote the victory.
Mail-in ballots are a moot point. This is a partisan article.
One thing I don't get, however, is that my understanding is that the states set the rules for the elections. Trying to put this issue at the federal level seems to be another moot point.