Interesting. I just talked to my mailman, who Amazon has delivering today despite the fed day off. No regular mail, just Amazon packages.
Anywho, two of my delayed packages showed up today and I asked him about it. It appears this is actually on Amazon's side and has been happening a lot here. Their delivery trucks have been routing packages to the wrong USPS distribution centers, so the packages sit an extra day until they get sent to the correct USPS distribution site for delivery to regional sites. That actually makes sense, as, looking at my tracking, the delayed packages were going to San Bernardino and Buena Park instead of Los Angeles. They then got routed back to Los Angeles and then upstate to my distribution center.