Problem with the serial connection between Processing and CircuitPython on an Adafruit Grand Central M4 Metro

Serial Connection Problem between Processing and CircuitPython Code on a Adafruit Grand Central M4 Metro.

I have a Adafruit Grand Central M4 Metro Micro-Computer with 3 Motors connected to it. On the Grand Central are to Files with CircuitPython Code on it. The first one is for the initialization of the 3 Motors and the Definition of the Movements of them. The Motors are connected to the Pins: D5, D6 ; D14, D15 ; D52, D53. The Code of the second File that imports the Code from the first File is for the Function of the Motors shown below:

import time
import board
from motor import *
import busio

uart = busio.UART(board.TX, board.RX, baudrate=9600)

def vorwärts():
    while True:
        motor1_R1(30)
        motor2_R2(30)

def rückwärts():
    while True:
        motor1_R2(30)
        motor2_R1(30)

def drehung_rechts():
    while True:
        motor1_R2(30)
        motor2_R2(30)
        motor3_R2(30)

def drehung_links():
    while True:
        motor1_R1(30)
        motor2_R1(30)
        motor3_R1(30)

while True:
    data = uart.readline()
    if data is not None:
        received_data = data.decode().strip()
        if received_data == 'L':
            drehung_links()
        elif received_data == 'R':
            drehung_rechts()
        

Now I want to controll these Functions with Buttons that I visualized in Processing. I am sending the Signals via the serial connection:

import processing.serial.*;

Serial myPort;

void setup() {
  size(400, 400); // Größe des Fensters festlegen
  
   String portName = "COM3";
  
  myPort = new Serial(this, portName, 9600); 
}

   if (mouseX > 50 && mouseX < 150 && mouseY > 50 && mouseY < 150) {
    // Linker Button wurde geklickt
    // Sende Signal über die serielle Schnittstelle
    myPort.write('L');
    println("Linker Button wurde geklickt");
  }
  
   if (mouseX > 250 && mouseX < 350 && mouseY > 50 && mouseY < 150) {
    // Rechter Button wurde geklickt
    // Sende Signal über die serielle Schnittstelle
    myPort.write('R');
    println("Rechter Button wurde geklickt");
  }

My Problem is that the Motors does not move at all if I press or hold one of the Buttons, but if I start a Function manuel in the CircuitPython Code, the Motors move, so the Problem must be the serial connection. Does anyone have an Idea what the Problem could be?