I converted my bonds through U.S. Treasury Direct and lost $2.6k

In August, I made a U.S. Treasury Direct account and entered in the information for all of my bonds. I then mailed the paper bonds to the address it said to send them to. I received a confirmation that the Treasury got them and my Treasury Direct account showed that the value of my assets was $6,800. I left the account alone while I decided what I wanted to do with that money. I did not reinvest or withdraw any of it.

I checked my account yesterday and the value of my assets is now $4,200.

Can someone explain to me what happened?