UVXY and TDA interesting situation today…

Yesterday sold this:

Sold UVXY Jan 18 2019 5.0/15.0 Bear call spreads @ 5.04

Email this morning saying I was assigned on 2 of the short 5 strike calls but…no short shares in the account and short calls are missing. Said he had a long list of accounts with the same issue. I’ll take the short position if they can make it work. Can cover the stock and re-sell the calls for a better gain than if nothing happened (as long as UVXY stays lower today). Waiting to hear the verdict from the guys researching the issue.