Why can't pending or partially filled auction orders be cancelled?
Pending and partially filled orders cannot be cancelled after the auction session ends. The exchange will automatically cancel them at around 4:30 PM. Also, if the client participates in the auction and the order is pending or partially filled, the shares cannot be sold in the normal market for the day.
Exchanges don't allow order modifications during the auction. Instead, the order must first be cancelled, and a new order with the updated price and quantity must be placed.