Arduino Nano and SIM800l, read SMS problem

I have an interesting and unsolvable problem.
I want to receive and read the message but this is happening when i use Arduino Nano (new bootloader). When i use Arduino Nano (old bootloader) everything is normal and everything works.
What should I do :frowning:

#include <SoftwareSerial.h>

//Create software serial object to communicate with SIM800L
SoftwareSerial mySerial(3, 2); //SIM800L Tx & Rx is connected to Arduino #3 & #2

void setup()
  //Begin serial communication with Arduino and Arduino IDE (Serial Monitor)
  //Begin serial communication with Arduino and SIM800L


  mySerial.println("AT"); //Once the handshake test is successful, it will back to OK
  mySerial.println("AT+CMGF=1"); // Configuring TEXT mode
  mySerial.println("AT+CNMI=1,2,0,0,0"); // Decides how newly arrived SMS messages should be handled

void loop()

void updateSerial()
  while (Serial.available()) 
    mySerial.write(;//Forward what Serial received to Software Serial Port
    Serial.write(;//Forward what Software Serial received to Serial Port

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