I am having a hard time to find why the widget is not updated in my project.
Because the project is too big to upload in this post, I made a simplified code.



Qt Code: 
  1. from PyQt5 import QtCore, QtGui, QtWidgets
  2. class Ui_Form(object):
  3.     def setupUi(self, Form):
  4.         Form.setObjectName("Form")
  5.         Form.resize(191, 223)
  6.         self.verticalLayoutWidget = QtWidgets.QWidget(Form)
  7.         self.verticalLayoutWidget.setGeometry(QtCore.QRect(0, 170, 191, 21))
  8.         self.verticalLayoutWidget.setObjectName("verticalLayoutWidget")
  9.         self.verticalLayout = QtWidgets.QVBoxLayout(self.verticalLayoutWidget)
  10.         self.verticalLayout.setContentsMargins(55, 0, 55, 0)
  11.         self.verticalLayout.setObjectName("verticalLayout")
  12.         self.saveButton = QtWidgets.QPushButton(self.verticalLayoutWidget)
  13.         self.saveButton.setStyleSheet("background-color: rgb(200, 200, 200)")
  14.         self.saveButton.setFlat(False)
  15.         self.saveButton.setObjectName("saveButton")
  16.         self.verticalLayout.addWidget(self.saveButton)
  17.         self.layoutWidget = QtWidgets.QWidget(Form)
  18.         self.layoutWidget.setGeometry(QtCore.QRect(0, 20, 191, 22))
  19.         self.layoutWidget.setObjectName("layoutWidget")
  20.         self.threadcountLayout = QtWidgets.QHBoxLayout(self.layoutWidget)
  21.         self.threadcountLayout.setContentsMargins(5, 0, 0, 0)
  22.         self.threadcountLayout.setObjectName("threadcountLayout")
  23.         self.label = QtWidgets.QLabel(self.layoutWidget)
  24.         sizePolicy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Preferred, QtWidgets.QSizePolicy.Preferred)
  25.         sizePolicy.setHorizontalStretch(0)
  26.         sizePolicy.setVerticalStretch(0)
  27.         sizePolicy.setHeightForWidth(self.label.sizePolicy().hasHeightForWidth())
  28.         self.label.setSizePolicy(sizePolicy)
  29.         self.label.setObjectName("label")
  30.         self.threadcountLayout.addWidget(self.label)
  31.         self.threadcountLineEdit = QtWidgets.QLineEdit(self.layoutWidget)
  32.         sizePolicy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Fixed, QtWidgets.QSizePolicy.Fixed)
  33.         sizePolicy.setHorizontalStretch(0)
  34.         sizePolicy.setVerticalStretch(0)
  35.         sizePolicy.setHeightForWidth(self.threadcountLineEdit.sizePolicy().hasHeightForWidth())
  36.         self.threadcountLineEdit.setSizePolicy(sizePolicy)
  37.         self.threadcountLineEdit.setMinimumSize(QtCore.QSize(25, 20))
  38.         self.threadcountLineEdit.setMaximumSize(QtCore.QSize(1, 20))
  39.         self.threadcountLineEdit.setMaxLength(3)
  40.         self.threadcountLineEdit.setObjectName("threadcountLineEdit")
  41.         self.threadcountLayout.addWidget(self.threadcountLineEdit)
  42.         self.label_2 = QtWidgets.QLabel(self.layoutWidget)
  43.         sizePolicy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Preferred, QtWidgets.QSizePolicy.Preferred)
  44.         sizePolicy.setHorizontalStretch(0)
  45.         sizePolicy.setVerticalStretch(0)
  46.         sizePolicy.setHeightForWidth(self.label_2.sizePolicy().hasHeightForWidth())
  47.         self.label_2.setSizePolicy(sizePolicy)
  48.         self.label_2.setObjectName("label_2")
  49.         self.threadcountLayout.addWidget(self.label_2)
  50.         self.retranslateUi(Form)
  51.         QtCore.QMetaObject.connectSlotsByName(Form)
  52.  
  53.     def retranslateUi(self, Form):
  54.         _translate = QtCore.QCoreApplication.translate
  55.         Form.setWindowTitle(_translate("Form", "Form"))
  56.         self.saveButton.setText(_translate("Form", "save"))
  57.         self.label.setText(_translate("Form", "HTTP thread count"))
  58.         self.threadcountLineEdit.setText(_translate("Form", "0"))
  59.         self.label_2.setText(_translate("Form", "s"))
  60.  
  61.  
  62. class Ui_MainWindow(object):
  63.     def setupUi(self, MainWindow):
  64.         MainWindow.setObjectName("MainWindow")
  65.         MainWindow.resize(331, 351)
  66.         sizePolicy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Fixed, QtWidgets.QSizePolicy.Fixed)
  67.         sizePolicy.setHorizontalStretch(0)
  68.         sizePolicy.setVerticalStretch(0)
  69.         sizePolicy.setHeightForWidth(MainWindow.sizePolicy().hasHeightForWidth())
  70.         MainWindow.setSizePolicy(sizePolicy)
  71.         MainWindow.setMinimumSize(QtCore.QSize(331, 351))
  72.         MainWindow.setMaximumSize(QtCore.QSize(331, 351))
  73.         MainWindow.setStyleSheet("background-color:rgb(250, 255, 151)")
  74.  
  75.  
  76. if __name__ == "__main__":
  77.     import sys
  78.     app = QtWidgets.QApplication(sys.argv)
  79.     MainWindow = QtWidgets.QMainWindow()
  80.     ui = Ui_MainWindow()
  81.     ui.setupUi(MainWindow)
  82.     MainWindow.show()
  83.     ui = Ui_Form()
  84.     ui.setupUi(MainWindow)
  85.     sys.exit(app.exec_())
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setupUi function of Ui_MainWindow is properly applied, but the one of Ui_Form is not applied.
How can I solve this problem?