When the TX and RX pins for Bluetooth are connected the LCD screen will not update. Why is that?
You connected the LCD module to serial hardware pins 0 (RX) and 1 (TX).

When you receive the data from the Bluetooth module, through the software serial, you send it to the hardware serial.

if(BTSerial.available()){
      recvChar = BTSerial.read();
      Serial.print(recvChar);
...


This messes up the communication with the LCD module. Remove Serial.print(recvChar); and it should work.



A more sensible solution would be to use hardware serial for the Bluetooth module and the other pins for the LCD module.

Software serial should only be used, if you really can't use the hardware serial, e.g. you need the hardware serial to communicate with another device (a PC or some other module).