Had a package with a somewhat valuable card (I purchased it for $150~ at the end of December, it’s now around $300-350) go missing with USPS. It said it had arrived at my post office on Jan 9 (awaiting delivery scan), so I gave them a few weeks to sort out the holiday blitz. When it never came I went in person 3 times over the past week to try and find it, but in the end the postmaster told me it was lost. Somehow it arrived at the destination post office safely, then just disappeared before it got delivered to my house 
The postmaster gave me an official form that said the package was lost that I sent over to the seller. I paid part of the total with eBay bucks, and noticed that the purchase was NOT eligible for buyer protector since I’d paid part of the purchase ($60~ out of the $150 total) with ebay bucks.
Still working things out with the seller, but just a word of caution on using those “free” bucks on items.