How can I switch window without crashing the program?

I am programming a GUI with Face Detection. My problem is that when I want to switch back to the main GUI (after Face Detection started), the program crashes after the GUI is loaded. The error message is: Process finished with exit code -1073740791 (0xC0000409)

After I click the Back button the GUI loads, but then it crashes...

My code for creating the GUIs (virtually Controller):

app = QApplication(sys.argv)
class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self.mainGUI()

    def registerGUI(self):
        self.registerui = registerwindow.Ui_RegisterWindow()
        self.registerui.setupUi(self)
        self.registerui.zurueck.clicked.connect(self.mainGUI)
        self.registerui.aufnahmestart.clicked.connect(self.TakePic)

    def loginGUI(self):
        self.loginui = loginwindow.Ui_LoginWindow()
        self.loginui.setupUi(self)
        self.loginui.zurueck.clicked.connect(self.mainGUI)
        self.loginui.pushButton_2.clicked.connect(self.dF)

    def mainGUI(self):
        self.mainui = mainwindow.Ui_MainWindow()
        self.mainui.setupUi(self)
        self.mainui.registrieren.clicked.connect(self.registerGUI)
        self.mainui.login.clicked.connect(self.loginGUI)

    def TakePic(self):
        exec(open("TakePic.py").read(), globals())

    def dF(self):
        exec(open("Gesichtserkennung.py").read(), globals())


window = MainWindow()
window.show()
sys.exit(app.exec_())

My code for the Face Detecction and embedding it into the GUI

path = "ImagesProject"
images = []
classNames = []
myList = os.listdir(path)

for element in myList:
    images.append(cv2.imread(path + "/" + element))
    classNames.append(element[:-4])


def findEncodings(images):
    encodingList = []
    for img in images:
        img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
        imgEncode = face_recognition.face_encodings(img)[0]
        encodingList.append(imgEncode)
    return encodingList


encodeListKnown = findEncodings(images)

app = QApplication(sys.argv)


class NewLoginWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self.newGUI()

    def newGUI(self):
        self.ui = loginwindow.Ui_LoginWindow()
        self.ui.setupUi(self)
        self.ui.zurueck.clicked.connect(self.mainGUI)

    def mainGUI(self):
        self.mainui = mainwindow.Ui_MainWindow()
        self.mainui.setupUi(self)

        # self.mainui.registrieren.clicked.connect(self.registerGUI)
        # self.mainui.login.clicked.connect(self.loginGUI)


print("1")
window = NewLoginWindow()

cap = VideoCapture(cv2.CAP_DSHOW)


def displayFrame():
    timer.start(60)
    success, frame = cap.read()
    frameS = cv2.resize(frame, (0, 0), None, 0.25, 0.25)
    frameS = cv2.cvtColor(frameS, cv2.COLOR_BGR2RGB)

    CurFrameFaceLocs = face_recognition.face_locations(frameS)
    CurFrameFaceLocEncode = face_recognition.face_encodings(frameS, CurFrameFaceLocs)

    for encode, loc in zip(CurFrameFaceLocEncode, CurFrameFaceLocs):
        matches = face_recognition.compare_faces(encodeListKnown, encode)
        faceDis = face_recognition.face_distance(encodeListKnown, encode)
        print(matches)
        print(faceDis)

        matchIndex = np.argmin(faceDis)
        print(matchIndex)

        if matches[matchIndex]:
            name = classNames[matchIndex].upper()
            print(name)
            y1, x2, y2, x1 = loc
            y1, x2, y2, x1 = y1 * 4, x2 * 4, y2 * 4, x1 * 4
            cv2.rectangle(frame, (x1, y1), (x2, y2), (0, 255, 0), 2)
            cv2.rectangle(frame, (x1, y2), (x2, y2), (0, 255, 0), cv2.FILLED)
            cv2.putText(frame, name, (x1 + 6, y2 - 6), cv2.FONT_HERSHEY_COMPLEX, 1, (255, 255, 255), 2)

        frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
        image = qimage2ndarray.array2qimage(frame)
        window.ui.label_4.setPixmap(QPixmap.fromImage(image))


window.show()
timer = QTimer()
timer.timeout.connect(displayFrame)
timer.start(60)I am programming a GUI with Face Detection. My problem is that when I want to switch back to the main GUI (after Face Detection started), the program crashes after the GUI is loaded. The error message is: `Process finished with exit code -1073740791 (0xC0000409)`

After I click the Back button the GUI loads, but then it crashes...

My code for creating the GUIs (virtually Controller):

app = QApplication(sys.argv)
class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self.mainGUI()

    def registerGUI(self):
        self.registerui = registerwindow.Ui_RegisterWindow()
        self.registerui.setupUi(self)
        self.registerui.zurueck.clicked.connect(self.mainGUI)
        self.registerui.aufnahmestart.clicked.connect(self.TakePic)

    def loginGUI(self):
        self.loginui = loginwindow.Ui_LoginWindow()
        self.loginui.setupUi(self)
        self.loginui.zurueck.clicked.connect(self.mainGUI)
        self.loginui.pushButton_2.clicked.connect(self.dF)

    def mainGUI(self):
        self.mainui = mainwindow.Ui_MainWindow()
        self.mainui.setupUi(self)
        self.mainui.registrieren.clicked.connect(self.registerGUI)
        self.mainui.login.clicked.connect(self.loginGUI)

    def TakePic(self):
        exec(open("TakePic.py").read(), globals())

    def dF(self):
        exec(open("Gesichtserkennung.py").read(), globals())


window = MainWindow()
window.show()
sys.exit(app.exec_())

My code for the Face Detecction and embedding it into the GUI

path = "ImagesProject"
images = []
classNames = []
myList = os.listdir(path)

for element in myList:
    images.append(cv2.imread(path + "/" + element))
    classNames.append(element[:-4])


def findEncodings(images):
    encodingList = []
    for img in images:
        img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
        imgEncode = face_recognition.face_encodings(img)[0]
        encodingList.append(imgEncode)
    return encodingList


encodeListKnown = findEncodings(images)

app = QApplication(sys.argv)


class NewLoginWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self.newGUI()

    def newGUI(self):
        self.ui = loginwindow.Ui_LoginWindow()
        self.ui.setupUi(self)
        self.ui.zurueck.clicked.connect(self.mainGUI)

    def mainGUI(self):
        self.mainui = mainwindow.Ui_MainWindow()
        self.mainui.setupUi(self)

        # self.mainui.registrieren.clicked.connect(self.registerGUI)
        # self.mainui.login.clicked.connect(self.loginGUI)


print("1")
window = NewLoginWindow()

cap = VideoCapture(cv2.CAP_DSHOW)


def displayFrame():
    timer.start(60)
    success, frame = cap.read()
    frameS = cv2.resize(frame, (0, 0), None, 0.25, 0.25)
    frameS = cv2.cvtColor(frameS, cv2.COLOR_BGR2RGB)

    CurFrameFaceLocs = face_recognition.face_locations(frameS)
    CurFrameFaceLocEncode = face_recognition.face_encodings(frameS, CurFrameFaceLocs)

    for encode, loc in zip(CurFrameFaceLocEncode, CurFrameFaceLocs):
        matches = face_recognition.compare_faces(encodeListKnown, encode)
        faceDis = face_recognition.face_distance(encodeListKnown, encode)
        print(matches)
        print(faceDis)

        matchIndex = np.argmin(faceDis)
        print(matchIndex)

        if matches[matchIndex]:
            name = classNames[matchIndex].upper()
            print(name)
            y1, x2, y2, x1 = loc
            y1, x2, y2, x1 = y1 * 4, x2 * 4, y2 * 4, x1 * 4
            cv2.rectangle(frame, (x1, y1), (x2, y2), (0, 255, 0), 2)
            cv2.rectangle(frame, (x1, y2), (x2, y2), (0, 255, 0), cv2.FILLED)
            cv2.putText(frame, name, (x1 + 6, y2 - 6), cv2.FONT_HERSHEY_COMPLEX, 1, (255, 255, 255), 2)

        frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
        image = qimage2ndarray.array2qimage(frame)
        window.ui.label_4.setPixmap(QPixmap.fromImage(image))


window.show()
timer = QTimer()
timer.timeout.connect(displayFrame)
timer.start(60)