Packages often get diverted to places we would think "out of the way" and re-routed by intent or error. The whole thing is sometimes a maze we can't easily figure out and when an anxious buyer sees that kind of unusual tracking they get scared. The first responder is correct about the hand-holding. Simple explanations, suppositions and good guesses can do a lot to help ease the buyer's anxiety. They want to know you're as concerned as they are.
I always tell them the package could be where it is because of weather issues or other unknown reasons but that USPS has always been very reliable for me and sometimes you just have to give them a little leeway. I say, "I would be happy to file a "lost mail" report, but even that, USPS won't start investigating until 2 weeks after the item was put into the system. By then it's usually delivered... we just need to give them a few days time." Assure the buyer you are watching the tracking too, and are aware of the situation and that you'll be happy to refund if the item isn't delivered by.... (pick a date 7 - 10 days from now)... and that they have absolutely nothing at risk. Check in with them every day if necessary, and assure them you are "on it" and that the package will arrive soon. "Just checked tracking on your package and it's in Wherever and headed your way!"
Reassuring the buyer takes some extra time, but it's way better than doing a refund, mail interception, whatever. 99% of the time the package will be delivered within a few days with no problems... even when you don't see any tracking activity. That is not at all uncommon.
