The Unity Quantum can service up to 20 ModbusTCP messages combined in a maximum configuration per CPU Scan.
A 140NOE771x1 in this system can service the maximum of 8 - Read Register or Write Register request.
But only 4 - Non Register type request. Messages are place if a message buffer and serviced is a FIFO (First-In/First-Out) fashion.
Power cycling or resetting the 140NOE771x1 module clears the message buffer.