still unsolved, but workaround by replacing the onewire with a DHT22 :P :P

this is my sketch:

// Gateway MySensors on NodeMCU with some Devices 
// OneWire for DS18B20 
// Bounce for S_DOOR (Rain Sensor)
#define MY_DEBUG
#define MY_BAUD_RATE 115200
#define MY_RADIO_NRF24

// #define MY_GATEWAY_SERIAL
#define MY_GATEWAY_ESP8266
#define MY_ESP8266_SSID "myWiFi"
#define MY_ESP8266_PASSWORD "******"
#define MY_ESP8266_HOSTNAME "sensor-gateway"
#define MY_PORT 5003
#define MY_GATEWAY_MAX_CLIENTS 3
#include <ESP8266WiFi.h>

#define MY_INCLUSION_MODE_FEATURE

#include <MySensors.h>
#include <SPI.h>
#include <DallasTemperature.h>
#include <OneWire.h>

#define COMPARE_TEMP 1 // Send temperature only if changed? 1 = Yes 0 = No
#define ONE_WIRE_BUS D1 // Pin where dallase sensor is connected 
#define MAX_ATTACHED_DS18B20 5

unsigned long temp_Sleep = 30000; // Sleep time between reads (in milliseconds)
unsigned long temp_nTime;

OneWire oneWire(ONE_WIRE_BUS); // Setup a oneWire instance to communicate with any OneWire devices
DallasTemperature sensors(&oneWire); // Pass the oneWire reference to Dallas Temperature. 
float lastTemperature[MAX_ATTACHED_DS18B20];
int numSensors=0;
bool receivedConfig = false;
bool metric = true;
// Initialize temperature message
MyMessage msgTemp(0,V_TEMP);

#include <Bounce2.h>
// RAIN Sensor Definitions and settings
#define CHILD_ID 10
#define BUTTON_PIN D4  // Arduino Digital I/O pin for button/reed switch
Bounce debouncer = Bounce(); 
int oldValue=-1;
MyMessage msgRain(CHILD_ID,V_TRIPPED);

unsigned long cTime;  // Current Time
void before()
{
  // Startup up the OneWire library
  sensors.begin();
}

void setup()  
{ 
  // requestTemperatures() will not block current thread
  sensors.setWaitForConversion(false);

  pinMode(BUTTON_PIN,INPUT);
  digitalWrite(BUTTON_PIN,HIGH);
  debouncer.attach(BUTTON_PIN);
  debouncer.interval(5);
}

void presentation() {
  // Send the sketch version information to the gateway and Controller
  sendSketchInfo("Temperature Sensor", "1.1");

  // Fetch the number of attached temperature sensors  
  numSensors = sensors.getDeviceCount();

  // Present all sensors to controller
  for (int i=0; i<numSensors && i<MAX_ATTACHED_DS18B20; i++) {   
     present(i, S_TEMP);
  }
  
  present(CHILD_ID, S_DOOR);  
}

void loop()     
{
  cTime = millis();  // Get current Timing

  if ((cTime - temp_nTime) >= temp_Sleep) {     // this is supposed to replace the sleep function 
    sensors.requestTemperatures();
    for (int i=0; i<numSensors && i<MAX_ATTACHED_DS18B20; i++) {
      float temperature = static_cast<float>(static_cast<int>(sensors.getTempCByIndex(i)));
      #if COMPARE_TEMP == 1
      if (lastTemperature[i] != temperature && temperature != -127.00 && temperature != 85.00) {
      #else
      if (temperature != -127.00 && temperature != 85.00) {
      #endif
        send(msgTemp.setSensor(i).set(temperature,1));
        lastTemperature[i]=temperature;
      }
    }
    temp_nTime = millis();
  }
  
  debouncer.update();
  int value = debouncer.read();
  if (value != oldValue) {
     // Send in the new value
     send(msgRain.set(value==HIGH ? 1 : 0));
     oldValue = value;
  }
  
}

if I enter a

Serial.print("Sensors Count over 1W bus: ");
Serial.println(sensors.getDeviceCount()); 

I got 0 :(

wirings are ok... I checked with the tester and I get correct voltage (3,3) and impedence (4,7k)
DHT works fine at first try on the same PIN

thanks for the help
ciao
Marco