Why is my qtstylesheets unload after a while?

I made a Class Frame which allows me not to recreate a frame every time I need it

Why is my qss unload after a while ?

I have no clue, why this is doing this, my main frame is going well with css, but this secondary frame is bugged.

I've tried to repaint(), update() nothing to do.

I'm using Windows 10 Pytohn 3.7 & PyQt5 5.15.0

frame with css loaded

frame with css unloaded

from PyQt5.QtWidgets import *
from PyQt5 import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *


class Frame(QWidget):

    TXT_COLOR = "#36d2f5"

    def __init__(self, parent=None, title='frame', titleBar=True, width=300, height=250):
        super(Frame, self).__init__(parent=parent)

        self.title = title
        self.titleBar = titleBar

        self.WIDTH = width
        self.HEIGHT = height
        self.TITLE_BARRE_HEIGHT = 25

        self.CONTENT = QWidget(self)

        self.initUI()


    def initUI(self):
        # CREATING MAIN FRAME
        # INIT frame attributes
        self.setWindowFlags(Qt.FramelessWindowHint)  # | Qt.WindowStaysOnTopHint)
        self.setStyleSheet('background-color: black; border-top-left-radius: 15px 15px; border-top-right-radius: 15px 15px;')
        self.setWindowOpacity(0.85)
        self.move(300, 300)
        self.setGeometry(0, 0, self.WIDTH, self.HEIGHT)
        self.setWindowTitle(self.title)
        self.setAttribute(Qt.WA_TranslucentBackground, True)


        self.CONTENT.show()
        self.CONTENT.move(0, 0)
        self.CONTENT.resize(self.WIDTH, self.HEIGHT)
        self.CONTENT.setStyleSheet("border-radius: 0px 0px; background-color: #101010; color: grey;")


        if self.titleBar == True:
            self.CONTENT.move(0, self.TITLE_BARRE_HEIGHT)
            self.CONTENT.resize(self.WIDTH, self.HEIGHT - self.TITLE_BARRE_HEIGHT)
            # CREATING TITLE BAR
            self.Title_BAR = QWidget(self)
            label_title = QLabel("__title__", self.Title_BAR)
            label_title.resize(self.WIDTH, self.TITLE_BARRE_HEIGHT)
            label_title.setAlignment(Qt.AlignCenter)
            label_title.setText(self.title)
            label_title.setStyleSheet("color: grey")

            self.Title_BAR.installEventFilter(self)
            self.Title_BAR.setStyleSheet('background-color: black')
            self.Title_BAR.setGeometry(0, 0, self.WIDTH, self.TITLE_BARRE_HEIGHT)
            self.Title_BAR.show()

            btnClose = QPushButton("", self)
            btnClose.move(self.WIDTH-20, 9)
            btnClose.resize(10, 10)
            btnClose.setStyleSheet("background-color:red; border-radius: 5px 5px;")
            btnClose.clicked.connect(self.close)

        layout = QVBoxLayout(self.CONTENT)

        # listbox
        self.listbox = QListWidget(self.CONTENT)
        self.listbox.setFont(QFont("System", 12))
        self.listbox.setStyleSheet("border:0px; color:" + self.TXT_COLOR)
        layout.addWidget(self.listbox)

        # Create textbox
        self.textbox = QLineEdit(self.CONTENT)
        self.textbox.setFocus()
        self.textbox.setStyleSheet("padding-left: 5px; border-radius: 7px 7px; background-color: black; color: cyan;")
        self.textbox.setFixedHeight(20)

        layout.addWidget(self.textbox)



    # ------------------------------------------------------------------------------------------------------------------
    # FRAME HANDLER
    def _show(self):
        self.initUI()
        self.update()
        self.repaint()
        self.show()

    def close(self):
        self.destroy()

    def eventFilter(self, obj, event):
        try:
            if event.type() == QEvent.MouseButtonPress:
                self.oldPos = event.globalPos()
            elif event.type() == QEvent.MouseMove:
                delta = QPoint(event.globalPos() - self.oldPos)
                self.move(self.x() + delta.x(), self.y() + delta.y())
                self.oldPos = event.globalPos()
            return QMainWindow.eventFilter(self, obj, event)
        except:
            pass