I will have to say, if there are ever any problems, it is due to the local Post Office.
While I have had nothing but excellent service and experience, some local post offices are just truly crap imo.
If things continue, just ask to speak to the post master and explain details.
More than likely they will listen, and things could change.
For mail, most offices do make two trips (one for letters, one for packages)
If tracking says out for delivery or delivered, always wait one day.
Some smaller offices may have a delay or backlog to be able to get it out promptly.
And now we have the holidays... always expect a delay, no matter what delivery service or company.