Brokers have to do MtoM settlement with NSCCL on a daily basis. Same is done by brokers on clients’ behalf on daily basis. This may be the reason F11 shows Buy/ Sell avg price based on Previous Day closing.
However, the back office will show the average price, calculation of which is done based on actual Buy/ Sell prices. Also you need to know that Buy/ Sell average prices in client’s Backoffice is updated at EOD after trade process is done by the broker.