As mentioned in “1.1.3.1 Broadcast message sequence” of "J-GATE3.0_Connectivity_Manual_Business_Message_part", J-GATE does not guarantee the order between different broadcast messages.
This is due to dissemination process of BO5 (Order reception and result notice) and BD6 (Trade Execution notice) operating in parallel, and in some circumstances messages may be reversed but this is unavoidable due to structure of J-GATE.