WHY THERE IS A DELAY IN QUOTATIONS ON THE STOCK EXCHANGE?
Exchange Nanex conducted research on the behavior of HFT traders after the Flash Crash, which occurred in 2010. Market manipulations by high-frequency traders were found, which included the rapid entry and removal of a large number of orders and attempts to create market confusion and trading opportunities for HFT traders themselves.
Trading robots delay price quotes while filling in the order book, simply placing and canceling orders at a speed substantially exceeding the capacity of the market data transmission channel on the exchange. Orders are accumulated in buffers, and the delay (increased delay) lasts until the buffer is exhausted. Such phantom orders with a speed of more than 10,000 messages per second , even for a fraction of a second, delay exchange channels.
https://www.youtube.com/watch?v=QSyV2y1zryY