UDP not working without start serial monitor

Hello
i have two arduino connected using ethernet communication Udp , the programm work fine when i open the serial monitor in sender Udp , i have the packetbuffer in the receiver Udp, but when i stop the serial monitor the communication Udp stopped
i want the communication still working , and i want to established the communication udp when the arduino get power

thank you

Hello

Best would be to share the Code?
Which arduino? Do you have a while (!Serial); in the setup() ?

thank you from your reply
yes i have a while (!Serial); in the setup() ?
but when i delete it , it not working
how the code can be working when the arduino get power
thank you sir

Which arduino do you have?
How are things wired?
Where is your code?