QComboBox not aligned with QPushButton

[fvez_demtroys]

Hi,

We are making an internal configuration tool using PyQt5 5.15.4.
Development is done on macOS Catalina 10.15.7
The final version will run on both OSX and Windows 10

I am having an issue where my QComboBox isn't aligning properly with my QPushButtons.
This issue is not present with a QLineEdit.

Here is a sample script allowing to showcase both situations.

import sys

from PyQt5.QtWidgets import *
from UI import Ui_mainWindow


class App(QMainWindow):
	def __init__(self):
		super(App, self).__init__()
		self.initUI()
		self.show()

	def initUI(self):
		self.mainWindow = Ui_mainWindow()
		self.mainWindow.setupUi(self)


class Ui_mainWindow(QMainWindow):
	def __init__(self):
		super().__init__()

	def setupUi(self, mainWindow):
		if not mainWindow.objectName():
			mainWindow.setObjectName(u"mainWindow")

		self.centralWidget = QWidget(mainWindow)
		self.centralWidget.setObjectName(u"centralWidget")
		self.baseGridLayout = QGridLayout(self.centralWidget)
		self.baseGridLayout.setObjectName(u"baseGridLayout")

		self.groupBox = QGroupBox(self.centralWidget)
		self.groupBox.setObjectName(u"groupBox")
		self.groupBox.setFlat(True)
		self.gridLayout = QGridLayout()
		self.gridLayout.setObjectName(u'gridLayout')
		self.gridLayout.setContentsMargins(10, 10, 10, 10)
		self.gridLayout.setSpacing(0)

		self.lineEdit = QLineEdit()
		self.lineEdit.setObjectName(u"lineEdit")
		self.lineEdit.setPlaceholderText('Placeholder Text')
		self.gridLayout.addWidget(self.lineEdit, 0, 0, 1, 3)

		self.pushButton_one = QPushButton()
		self.pushButton_one.setObjectName(u"pushButton_one")
		self.pushButton_one.setText('One')
		self.gridLayout.addWidget(self.pushButton_one, 1, 0, 1, 1)

		self.pushButton_two = QPushButton()
		self.pushButton_two.setObjectName(u"pushButton_two")
		self.pushButton_two.setText('Two')
		self.gridLayout.addWidget(self.pushButton_two, 1, 2, 1, 1)

		self.emptyLabel = QLabel()
		self.emptyLabel.setObjectName(u"emptyLabel")
		self.gridLayout.addWidget(self.emptyLabel, 2, 0, 1, 1)

		self.comboBox = LabelAndComboBox(self.groupBox)
		self.comboBox.setObjectName(u"comboBox")
		self.gridLayout.addWidget(self.comboBox, 3, 0, 1, 3)

		self.pushButton_three = QPushButton()
		self.pushButton_three.setObjectName(u"pushButton_three")
		self.pushButton_three.setText('Three')
		self.gridLayout.addWidget(self.pushButton_three, 4, 0, 1, 1)

		self.pushButton_four = QPushButton()
		self.pushButton_four.setObjectName(u"pushButton_four")
		self.pushButton_four.setText('Four')
		self.gridLayout.addWidget(self.pushButton_four, 4, 2, 1, 1)

		self.groupBox.setLayout(self.gridLayout)

		self.setCentralWidget(self.centralWidget)

		mainWindow.setCentralWidget(self.centralWidget)
		self.baseGridLayout.addWidget(self.groupBox, 0, 0, 1, 1)


class LabelAndComboBox(QWidget):
	def __init__(self, parent=None):
		super(QWidget, self).__init__(parent)
		self.layout = QVBoxLayout(self)
		self.layout.setContentsMargins(0, 0, 0, 0)

		self.label = QLabel('Label Text')

		self.comboBox = QComboBox()
		self.comboBox.addItems(['item one', 'item two', 'item three'])

		self.layout.addWidget(self.label)
		self.layout.addWidget(self.comboBox)


if __name__ == "__main__":
	app = QApplication(sys.argv)
	ex = App()
	sys.exit(app.exec_())

When you run the script, you can clearly see that the QLineEdit is aligned correctly with the QPushButton and that the QComboBox is not aligned correctly.
Any idea why?

Thanks in advance,
FVez

[fvez_demtroys]

Here are some images to help visualize the issue.

[fvez_demtroys]

Does anyone know how to handle this?