I don't recall all of the reasons that the NY primary mail-in ballots went south, although my recollection is that a big one was the absence of a postmark on a ballot that arrived after election day. Sadly, that's a problem that's only fixable by getting the P.O. to actually apply the postmarks, which isn't always what happens when it's prepaid postage.

Sorry for the necessity for swearing.

I have occasionally had my ballot pop out of the machine for an undervote. It was always an *intentional* undervote, but...