There’s clearly a ripple under the surface - and not all shorts are in the statistics?
FTD thus refers to shares that could not be delivered to the buyer on the agreed settlement date of the trade.
At that time, on the Nvidia trading day, nearly 3 million shares were not delivered by some party. Generally, this is considered an indication of very aggressive short-selling activity - perhaps it wasn’t confirmed whether shares could be borrowed before selling, i.e., was naked short selling behind it?