UART strange echo problem

[JustVic]

hardware:
- ESP32C3 mini board
- sim808 development board
- usb-ttl adapter

I am receiving back a copy of the data I sent via UART. like echo

Two tasks are running simultaneously: one for reading data from UART and the other for sending a command. Every 10 seconds, I send the 'AT' command to the SIM808 module, and in response, it sends back 'OK'. However, in my debug console, I also see the command I sent. Additionally, I connected a USB-TTL adapter to the TX of the SIM808 to monitor the module's response on another screen, and there I do not see this 'echo'.

esp debug output:

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I (580294) UART: Length: 10
AT

OK
I (590294) UART: Length: 10
AT

OK

usb-ttl adapter output:

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23:48:18.436 -> 
23:48:18.436 -> OK
23:48:28.439 -> 
23:48:28.439 -> OK

If I switch the RX pin from the ESP to the USB-TTL and manually send the same command by ttl adapter, the outputs will be identical.

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I (20524) UART: Length: 6

OK
I (24214) UART: Length: 6

OK

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23:53:19.170 -> 
23:53:19.170 -> OK
23:53:22.880 -> 
23:53:22.880 -> OK

My code below is almost entirely taken from the uart_echo example.

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#include <stdio.h>
#include <driver/uart.h>
#include <string.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_log.h"
#include "sdkconfig.h"

#define ECHO_TEST_TXD (21)
#define ECHO_TEST_RXD (20)

#define ECHO_UART_PORT_NUM      UART_NUM_1
#define ECHO_UART_BAUD_RATE     115200


static const char *TAG = "UART TEST";

#define BUF_SIZE (200)

void uart_init() {
    uart_config_t uart_config = {
            .baud_rate = ECHO_UART_BAUD_RATE,
            .data_bits = UART_DATA_8_BITS,
            .parity    = UART_PARITY_DISABLE,
            .stop_bits = UART_STOP_BITS_1,
            .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
            .source_clk = UART_SCLK_DEFAULT,

    };
    uart_param_config(ECHO_UART_PORT_NUM, &uart_config);
    uart_set_pin(ECHO_UART_PORT_NUM, ECHO_TEST_TXD, ECHO_TEST_RXD, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE); // Піни RX і TX
    uart_driver_install(ECHO_UART_PORT_NUM, BUF_SIZE * 2, 0, 0, NULL, 0);
}

void printData(uint8_t *data);

void uart_read_task(void *pvParameter) {
    uint8_t *data = (uint8_t *) malloc(BUF_SIZE);
    if (data == NULL) {
        ESP_LOGE("UART", "Memory allocation failed");
        vTaskDelete(NULL);
        return;
    }

    while (1) {
        int length = uart_read_bytes(ECHO_UART_PORT_NUM, data, BUF_SIZE - 1, 20 / portTICK_PERIOD_MS);
        if (length > 0) {
            data[length-2] = 0; // delete \r\n
            ESP_LOGI("UART", "Length: %d", length);

            printData(data);
        }
    }
}

void printData(uint8_t *data) {
    int i = 0;
    char c = data[i];
    while (c != '\0') {
        if (c >= 32 || c == 10) {
            if (c == 10) {
                printf("\n");
            } else {
                printf("%c", c);
            }
        }
        c = data[++i];
    }
    printf("\n");
}

void uart_write_task(void) {
    const char *command = "AT\r\n";
    while (1) {
        uart_write_bytes(ECHO_UART_PORT_NUM, command, strlen(command));
        vTaskDelay(10000 / portTICK_PERIOD_MS);
    }
}

void app_main(void)
{
  uart_init();
  xTaskCreate(uart_read_task, "uart_read_task", 2048, NULL, 9, NULL);
  xTaskCreate(uart_write_task, "uart_write_task", 2048, NULL, 8, NULL);
}