If we consider voting to be a period of weeks rather than a day (absentee, early voting & election day), then any vote cast legally during that time is valid, and we don't have to have edge cases where a vote was initially valid, but then invalid, but yet have no way to actually remove them.
What's worse is then people argue that we should make Election Day a national holiday, as if that would actually improve turnout (HINT: Ask your local retail, food, or other service worker how easy it is for them to get other holidays like Labor Day or Memorial Day off)
Mail-in voting is great, but I acknowledge that a lot of people don't trust it.
So why don't we do the actual best thing? Make voting open for multiple days. If you need to vote in person, then it only makes sense to keep polls open long enough so that no matter what job you do, no matter what shift you work, you should be able to find the time to vote.
IMO, making the polls open 24 hours for 3 days, or maybe 9 AM to 9 PM for a week, should cover basically everyone except those that travel a lot for their jobs (ie, long haul truckers), but they'd be voting absentee anyways.
So the short answer is "yes; states disagreed on whether it was secure." The longer answer is that states that were doing it didn't have any mathematically-detectable fraud patterns distinguishing them from states that didn't, and states that just started in 2016 didn't seem to have any major systemic execution issues that would suggest fraud occurred.
We even have a category for it now: essential workers would be the only ones who aren't banned.