[BogeyBoy]

I would go down and talk to the person who delivers your mail and ask them if there is some problem.

Perhaps -

1. One of your neighbors is on a vacation mail hold and the carrier accidentally held your mail with theirs. (Not necessarily your physical neighbor, but someone whose mailbox is adjacent to yours. Or someone with a similar address - you're at 222 Adams St and they are at 222 Eden St. Or someone with a similar name, you are Ted Jones and they are Tad Jones.)

2. Your mail had been on hold in the past and the substitute carrier was still holding it - that's why it only happened occasionally.

Unfortunately mail handling at the delivery level is a manual operation. That leaves the door open for many variations of human error.

Hopefully your carrier will be able to answer your questions and help you.