USPS and UPS/FEDEX have different destinations.

Make sure that you addressed correctly depending on your carrier. USPS goes to a po. box and the others go directly (it seems). If USPS tried to deliver today (saturday) to the wrong place (not po. box), you will have to reschedule delivery (they don't attempt anymore on their own) or hope that USCIS puts the order in (good luck with that).

That's not true USPS Express does not go to P.O. box
See link.

Lol, tell me about it. I went to the U.S postal office to mail mine today (saturday) and the lady was explaining to me it'd be pointless to send it Express because tomorrow is sunday anyway and they don't deliver on sundays. So she told me if I sent it Priority Mail instead, the estimated arrival would be Monday anyway, so I went with that. But thennn, I was so stressed out already and originally had my mind set on Express Mail, that I ended up putting the wrong Chicago address for Priority Mail (I put the non P.O. Box one). So When I got home, I realized I had made the mistake and had to run back there and thank god my package was still there but they already had it in the back for processing but anyway, the lady was able to retrieve my package and I fixed it to be sent as Priority Mail to the Chicago, IL lockbox with the P.O. Box number. Phew D:

you're right, I thought I read UPS on the heading. Anyway, if they attempted delivery today, you'll still have to reschedule (or expect USCIS to do so).