It's only USPS that doesn't seem to come through? What about other short code text messages (i.e., messages from 5 or 6 digit phone numbers)?
Come to think of it, I didn't get a text from Amazon either when something shipped. So maybe those short hand numbers all got blocked? How do I get them unblocked? This is so stupid! It was working just fine!
Try resetting your network connections. Settings > connections > more connection settings > reset network connections. (thank you Mustang 7757) I had problems after that same update. Reset all my connections and haven't had any problems. And I just tracked packages via Post office and from Amazon both by text.
The only drawback is you'll have to re synch all Bluetooth connections and re-enter all your WiFi passwords again.