Checkable QComboBox will lost some item after scroll down

Question

There is a Checkable QComboBox that wrote in python. But after I scroll the items down (don't scroll back!) and pack up the drop down area and scroll it down again some items will disappear! My PyQt version is 5.15.0.

There is the code. Copy and run , you will find this phenomenon. I think this might be a bug of QListWidget, but don't find anyone asked about it.

from PyQt5.QtWidgets import QComboBox,QLineEdit,QListWidget,QCheckBox,QListWidgetItem,QApplication, QLabel, QMainWindow
import sys

list_=["1","2","3","4","5","6","7","8","9","10","11"]#

class MainWindow(QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.resize(320, 100)
        self.setWindowTitle("aaaa")
        self.setStyleSheet(
            """
            QMainWindow
            {
                background-color:white;
                color:white;
                margin:0px
            }
            """
        )
        self.InitializeWindow()
        self.i = 0

    def InitializeWindow(self):
        comb=ComboCheckBox(list_, self)
        comb.show()
        pass


class ComboCheckBox(QComboBox):
    def __init__(self,items, parent):#items==[str,str...]
        super(ComboCheckBox,self).__init__(parent)
        self.items=items
        self.items.insert(0,'all')
        self.row_num=len(self.items)
        self.Selectedrow_num=0
        self.qCheckBox=[]
        self.qLineEdit=QLineEdit()
        self.qLineEdit.setReadOnly(True)
        self.qListWidget=QListWidget()
        self.addQCheckBox(0)
        self.qCheckBox[0].stateChanged.connect(self.All)
        for i in range(1,self.row_num):
            self.addQCheckBox(i)
            self.qCheckBox[i].stateChanged.connect(self.show)
        self.setModel(self.qListWidget.model())
        self.setView(self.qListWidget)
        self.setLineEdit(self.qLineEdit)         
 
    def addQCheckBox(self,i):
        self.qCheckBox.append(QCheckBox())
        qItem=QListWidgetItem(self.qListWidget)
        self.qCheckBox[i].setText(self.items[i])
        self.qListWidget.setItemWidget(qItem,self.qCheckBox[i])        
 
    def Selectlist(self):
        Outputlist=[]
        for i in range(1,self.row_num):
            if self.qCheckBox[i].isChecked()==True:
                Outputlist.append(self.qCheckBox[i].text())
        self.Selectedrow_num=len(Outputlist)
        return Outputlist 
 
    def show(self):
        show=''
        Outputlist=self.Selectlist()
        self.qLineEdit.setReadOnly(False)
        self.qLineEdit.clear()
        for i in Outputlist:
            show+=i+';'
        if self.Selectedrow_num==0:
            self.qCheckBox[0].setCheckState(0)
        elif self.Selectedrow_num==self.row_num-1:
            self.qCheckBox[0].setCheckState(2)
        else:
            self.qCheckBox[0].setCheckState(1)
        self.qLineEdit.setText(show)
        self.qLineEdit.setReadOnly(True)
 
    def All(self,status_):
        if status_==2:
            for i in range(1,self.row_num):
                self.qCheckBox[i].setChecked(True)
        elif status_==1:
            if self.Selectedrow_num==0:
                self.qCheckBox[0].setCheckState(2)
        elif status_==0:
            self.clear()
 
    def clear(self):
        for i in range(self.row_num):
            self.qCheckBox[i].setChecked(False)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())