This is gist to reproduce the problem i'm facing with PyQt5 and VisPy

layout_problem.py

"""This gist created to demonstrate an layout error, however, problem is solved with switching to anaconda/python
"""
import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QSlider, QScrollArea, QFrame, QPushButton
from PyQt5.QtWidgets import QVBoxLayout, QHBoxLayout
from vispy.scene import SceneCanvas, PanZoomCamera


class Left(QHBoxLayout):
    def __init__(self):
        super().__init__()
        self.addWidget(QSlider(Qt.Vertical))
        self.addWidget(QSlider(Qt.Vertical))


class Right(QFrame):
    def __init__(self):
        super().__init__()
        dim_buttons_layout = QHBoxLayout()
        dim_buttons_layout.addWidget(QPushButton("1D"))
        dim_buttons_layout.addWidget(QPushButton("2D"))
        dim_buttons_layout.addWidget(QPushButton("3D"))

        Right_layout = QVBoxLayout()
        Right_layout.addLayout(dim_buttons_layout)
        Right_layout.addWidget(QPushButton("asdF"))
        Right_layout.addWidget(QPushButton("fdsA"))

        self.setLayout(Right_layout)


class Viewer(QWidget):
    def __init__(self):
        super().__init__()
        self.canvas = SceneCanvas(keys=None, vsync=True)

        layout = QVBoxLayout(self)
        layout.setContentsMargins(0, 0, 0, 0)
        self.setLayout(layout)

        # layout.addWidget(self.canvas.native)

        self.view = self.canvas.central_widget.add_view()
        self.view.camera = PanZoomCamera(aspect=1)
        self.view.camera.flip = (0, 1, 0)
        self.view.camera.set_range()


class Window:
    def __init__(self):
        self._qt_window = QMainWindow()
        self._qt_central_widget = QWidget()
        self._qt_window.setCentralWidget(self._qt_central_widget)
        self._qt_central_widget.setLayout(QHBoxLayout())
        self._qt_window.statusBar().showMessage('Ready For Action')

    def add_viewer(self):
        left = Left()
        right = Right()
        viewer = Viewer()
        self._qt_central_widget.layout().addLayout(left)
        self._qt_central_widget.layout().addWidget(viewer)
        self._qt_central_widget.layout().addWidget(right)

    def resize(self, *args):
        self._qt_window.resize(*args)

    def show(self):
        self.resize(self._qt_window.layout().sizeHint())
        self._qt_window.show()
        self._qt_window.raise_()


def main():
    win = Window()
    win.add_viewer()
    win.show()
    return win

if __name__ == '__main__':
    application = QApplication(sys.argv)
    main_win = main()
    sys.exit(application.exec_())