Hello,
I've opened a UDP server in one machine and the UDP client in another machine, the client sends a message every second and I don't see this behaviour.
I'm using the demo in the folder: "Demos\35.P2P\01.UDP_Server_Client", just modified with a TTimer in the UDP client.
To check which ports are opened I'm using TCPView, which can be downloaded from:
https://learn.microsoft.com/es-es/sysinternals/downloads/tcpview
I don't know why it's happening, try to identify which application is blocking these ports, maybe an antivirus or firewall?
Kind Regards,
Sergio