LiquidCrystal_i2c and Pin 2
LiquidCrystal_I2C    lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);


Are you not using pin 2 in the LiquidCrystal_I2C constructor? So you can't also use it for the DHT sensor.



I withdraw that suggestion.



Can you please try saving some RAM?

Use the F macro with your prints, eg.

  Serial.print(F("Humidity: ")); 
  Serial.print(DHT_hum);
  Serial.print(F(" %\t"));
  Serial.print(F("Temperature: ")); 


Ditto with the lcd.print() calls.