Same happened to me - I handed my mailman numerous packages during that same week and 95% of them were not scanned for over a week - a few took longer. One buyer did file a INR even though I had messaged her with details of the situation. On the other hand some of my buyers were incredibly understanding. I mailed my grandson Christmas presents - never did scan and I was the most upset about this one package. It FINALLY arrived on Wednesday - January 6th.Ebay is supposedly supporting sellers in encouraging buyers to wait to file an INR case or just requesting a refund. I had a similar situation to @BeenBurned. Package picked up 11/30, not scanned at all until 12/14--two full weeks. You shouldn't have to refund and ebay should not insist. Ask your buyer to be patient; tell you buyer you'll make it right but please wait for the scans.
You can also go online to the USPS website and open an inquiry. It will show up on your ebay tracking and may help the buyer be patient. Go to this page: https://www.usps.com/help/missing-mail.htm and complete the missing mail form. As the sender, only you can complete this anyway. Then tell the buyer what you've done and, again, request patience.
Interesting.....I stood in line just to have my package (a pricey ebay sale) scanned on Sat. - Jan. 2nd. It should have arrived two states away on Tuesday. Jan. 5th. It made it TO THE TOWN on the label early Tuesday morning and expected the scan to read next.....”on truck for delivery.” .....seriously it then begin to move state to state to state all along the east coast. The scenic USPS tour. Right now it is back in MY TOWN. Thank goodness I waited in line for it to scan and I can at least see where it is.