Problems with openGL and PyQt5

I am moving from Winpython3.4.3.7Qt4 to Winpython3.x.x.xQt5 (I tried a bunch of versions), and I am having the following problem:

The following minimal code (it does nothing usable, but demonstrates the error):

from PyQt5 import QtWidgets
import OpenGL.GL as gl
from PyQt5.QtOpenGL import QGLWidget
qapp = QtWidgets.QApplication([])
window = QGLWidget()
window.makeCurrent()
index = gl.glGenLists(1)
print(index)

runs on all my machines with Winpython3.4.3.7Qt4 and prints '1'. It does not, however, run on all machines when I use Winpython3.x.x.xQt5. The error I get is:

Traceback (most recent call last):
  File ".\opengl.py", line 12, in <module>
    index = gl.glGenLists(1)
  File "C:\Winpython-64bit-3.6.7.0\python-3.6.7\lib\site-packages\OpenGL\platform\baseplatform.py", line 405, in __call__
    return self( *args, **named )
  File "C:\Winpython-64bit-3.6.7.0\python-3.6.7\lib\site-packages\OpenGL\error.py", line 232, in glCheckError
    baseOperation = baseOperation,
OpenGL.error.GLError: GLError(
        err = 1282,
        description = b'invalid operation',
        baseOperation = glGenLists,
        cArguments = (1,),
        result = 0
)

I have the feeling that window.makeCurrent() isn't coming through, but I have no idea why. What changed in that regard from Qt4 to Qt5?

from Problems with openGL and PyQt5