Multiplexing HID and serial on ATMega32U4

Question

I designed a custom ATMega32U4 based Arduino Leonardo board. I'm using MHeironimus/ArduinoJoystickLibrary to implement an HID joystick. I need to create also a virtual serial port to send NON joystick data to the USB host (Android device). If I try to set use the usb serial the joystick device is not recognized. If I stop the serial the joystick works fine. This's the code:

#include <Arduino.h>
#include <Joystick.h>
#define JOYSTICK_PERIOD 20
const int BUTTON1_PIN = 4;
const int BUTTON2_PIN = 5;
int x = 0, y = 0, rx = 0, ry = 0, din = 0;
long time1, time2;
Joystick_ Joystick(
  JOYSTICK_DEFAULT_REPORT_ID, 
  JOYSTICK_TYPE_GAMEPAD,
  2, 0,
  true, true, false,
  true, true, false,
  false, false,
  false, false, false
);
void setup()
{
  pinMode(4, INPUT_PULLUP);
  pinMode(5, INPUT_PULLUP);
pinMode(A0, INPUT);
  pinMode(A1, INPUT);
  pinMode(A2, INPUT);
  pinMode(A3, INPUT);
Joystick.begin();
  Joystick.setXAxisRange(0, 1000);
  Joystick.setYAxisRange(0, 1000);
  Joystick.setRxAxisRange(0, 1000);
  Joystick.setRyAxisRange(0, 1000);
time1 = millis();
Serial1.begin(9600);
  Serial.begin(9600);
}
void SerialEvent()
{
  int _count = Serial.available();
for(int _i=0;_i<_count;_i++)
    Serial1.write(Serial.read());
}
void Serial1Event()
{
  int _count = Serial1.available();
for(int _i=0;_i<_count;_i++)
    Serial.write(Serial1.read());
}
void loop() 
{
  time2 = millis();
long _period = time2 - time1;
time2 = time1;
if(_period >= JOYSTICK_PERIOD)
  {
    din = (digitalRead(BUTTON1_PIN) << 1) | digitalRead(BUTTON2_PIN);
x = analogRead(A0);
y = analogRead(A1);
rx = analogRead(A2);
ry = analogRead(A3);

Joystick.setButton(0, din);

Joystick.setXAxis(x);
Joystick.setYAxis(y);
Joystick.setRxAxis(rx);
Joystick.setRyAxis(ry);

}
}

Anyone has hints?