ESP-WROOM-02 responding strange to AT commands

Using Arduino Programming Questions
1

Hello,
I using the ESP-WROOM-02 (esp8266 core) as WIFI module and the Arduino nano IOT 33 (samd21g18) as main processing unit. I flashed the ESP-WROOM-02 via the ESP flash download tool with the AT Firmware v2.2.1.0 . The user guide highlights that the default ESP8266 RTOS AT firmware for ESP-WROOM-02 swaps RX/TX with CTS/RTS.

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For testing the UART, I used the Arduino Serial monitor and the UART connected to the on-board FTDI. To link the new pins (IO15 and IO13) , I connected the pin RX0 to IO13 and the TX to IO15 as a bypass.
When I sent any AT command (or any thing that I wrote on serial) the ESP always returned an empty line and a new line saying ready. Fist I tough that was the CR and line ending, I tried all combinations a didn´t worked.

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To understand was happening I connected a logic analyser to RX0 in order to check if was the same as what I was sending via serial monitor. And it was sending right.

Then, I connected the logic to the IO15 (ESP TX). But something appeared wrong. The first message is missing a bit.

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I tested then using an arduino nano iot 33 (uses 3.3V level) to send the AT commands to ESP. I connected directly the arduino to IO15 and IO13 but the result was worst, since the ESP didn´t replied anything to the arduino.
The code:

#include <Arduino.h>
#include "wiring_private.h"

//see https://github.com/ostaquet/Arduino-Nano-33-IoT-Ultimate-Guide
Uart Serial0 (&sercom0, 5, 6, SERCOM_RX_PAD_1, UART_TX_PAD_0);
String a;

// Attach the interrupt handler to the SERCOM
void SERCOM0_Handler()
{
    Serial0.IrqHandler();
}



void setup() {
  pinMode(LED_BUILTIN, OUTPUT);      // set LED pin as output
  digitalWrite(LED_BUILTIN, LOW);    // switch off LED pin

  // Reassign pins 5 and 6 to SERCOM alt
  pinPeripheral(5, PIO_SERCOM_ALT);
  pinPeripheral(6, PIO_SERCOM_ALT);



  Serial.begin(115200);               // initialize serial communication at 9600 bits per second:

  // Start my new hardware serial
  Serial0.begin(115200);


}


void loop() {



      Serial0.println("AT+GMR");
      while (Serial0.available()) {
        a = Serial0.readString();
        Serial.print(a);
      }
      delay(1000);


  }

The result from Arduino TX

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The ESP TX, in other hand, does not reply at all. Also I tried to slow the baud rate to 9600 (at the user guide says to test with 115200). note that I have the grounds connect to each board.
Any help would be grateful.

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