For the past two Fridays, IB didn't execute two orders sent at 15.40 CST on the ZN future contract. Any idea what is going on? The same type of order was executed earlier in the same day and on the same contract, and also at the end of previous trading sessions not on Fridays (15.40 is close to 16.00, which is the end of the session) I read the audit trail and it listed the "PlaceOrder" line but the "Acknowledged" and the "Filled" section were missing. I wonder if anyone could guess or knows the reason of these failed executions. Have there been any recent changes in the ZN trading schedule (especially on Friday before the close)? Or in the way IB handles these related orders? Thank you. I will try to send the order 15 minutes earlier on friday and this might solve the problem, but I would also like to know why it happened.