Getting "Qt: Session management error: Could not open network socket" and segmentation fault in Mayavi

With Mayavi in Python 2.7.13 and Ubuntu 17.04 I get

>>> import mayavi.mlab
Qt: Session management error: Could not open network socket

>>> mayavi.mlab.text3d(0, 0, 0, 'Hello')
Segmentation fault (core dumped)

On the command-line prompt I get

$ mayavi2
Segmentation fault (core dumped)

I am using a pip-install version and tried:

sudo pip install --upgrade --force-reinstall mayavi
sudo pip install --upgrade --force-reinstall pyface

with strace mayavi2 the segmentation fault occurs near

 open("/usr/lib/x86_64-linux-gnu/libQtCore.so.4", O_RDONLY|O_CLOEXEC) = 15

I suspect there is some kind of incompatibility here?