Arduino Yun receives UDP packets, but fails to send

I have an Arduino Yun connected via ethernet to my PC.
Although I receive successfully UDP packets from my PC, I can’t send UDP packets from Arduino to my PC.

This is my code:

#include <Process.h>
#include <BridgeUdp.h>

BridgeUDP Udp;

IPAddress IP(172, 31, 92, 10); //MY PC'S IP

void setup() {
  Bridge.begin();       
  Udp.begin(9911); 
  Serial.begin(9600);
}

void loop() {

  //TAKES UDP - PRINTS TO SERIAL
  if (Udp.parsePacket()) {
    int udp_received = Udp.available();
    char udp_buffer[udp_received + 1];
    Udp.read(udp_buffer, udp_received);
    udp_buffer[udp_received] = '\0';
    Serial.println(udp_buffer);
  }

    //SENDING UDP TO PC (TESTING)
    char udp[] = "test";
    Udp.beginPacket(IP, 9911);
    Udp.write(udp, sizeof(udp));
    Udp.endPacket();
    delay(1000);
}

I send UDP packets from PC to Arduino using ncat -u 172.31.92.3 9911.
Then I use ncat -lu 172.31.92.10 -p 9911 to set up a UDP listening server on my PC, but I receive nothing from Arduino.

UPDATE:

Monitoring the connection with Wireshark shows that UDP packets from Arduino Yun to PC are actually sent, but I still can’t see them in the console of the listening server.

Doesn't sizeof(udp) refer to the size of the char pointer, not the size of the string? Perhaps you were thinking of strlen()?

aarg:
Doesn't sizeof(udp) refer to the size of the char pointer, not the size of the string? Perhaps you were thinking of strlen()?

I tried strlen() too, but it doesn't work.
I tried to copy-paste the reference of the write function but it appears very strange in the preview, so I'll post the link: Bridge/BridgeUdp.cpp at master · arduino-libraries/Bridge · GitHub

"it doesn't work"... doesn't tell me much. What happens, or doesn't happen?

Does this thread suggest anything?

aarg:
"it doesn't work"... doesn't tell me much. What happens, or doesn't happen?

Does this thread suggest anything?
https://forum.arduino.cc/index.php?topic=497555.0

"It doesn't work" -> udp listening server receives nothing from arduino.
I have done everything the link says long time ago.