napari: QOpenGLWidget is not supported on this platform.

Using pyqt 5.9.2 on an Ubuntu 18.04 machine with the miniconda3 python 3.6.9 distribution, I launch IPython via ipython --gui=qt5, and get

import napari
~/miniconda3/lib/python3.6/site-packages/napari/__init__.py:27: UserWarning:
    napari was tested with QT library `>=5.12.3`.
    The version installed is 5.9.6. Please report any issues with this
    specific QT version at https://github.com/Napari/napari/issues.

from skimage.data import astronaut

viewer = napari.view_image(astronaut(), rgb=True)
WARNING: QOpenGLWidget is not supported on this platform.
WARNING: This plugin does not support propagateSizeHints()

and nothing is displayed on-screen.