Do you live in an overly Jewish and/or safe neighborhood? It has happened to me numerous times in Lakewood that the envelope didn't show up. Most times it came a day or two later. Once, it was delivered to the wrote address, but that resident returned it to me.
I can get mail form neighbors, happens all the time.
Concern here is, 2 days in a row, everything else arrived, just 2 checks didn't.