My current assumption is that there is a incompatibility with the BH1750 sensor library. When I set the symbols "LOCAL_SENSORS" and "LOCAL_SENSORS_BME280" it works. I will continue tomorrow evening...

@tekka No, but I can do that...

It works as well. Thanks again!

Here is the code:

// Before radio initialization
void preHwInit() 
{
  Serial.begin(57600);
  Serial.println("preHwInit()");

  Wire.begin(D3, D4);
  i2cdetect();

  Serial.println("Init: BME280 (Temperature, Humidity, Pressure)");
  if (!bme.begin(0x77)) {
    Serial.println("Could not find a valid BME280 sensor, check wiring!");
    while (1);
  }

  Serial.println("Init: BH1750 (Light)");
  lightSensor.begin();
}

setup() is empty.