napari: Installation problems - ubuntu 20.04

Installing via pip into a clean conda environment as follows:

conda create -y --name napariB python=3.8 ipython
conda activate napariB
pip install  'napari[all]'

> ipython --gui=qt
Python 3.8.5 (default, Sep  4 2020, 07:30:14) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.20.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: /home/richard.beare/miniconda3/envs/napariB/bin/python: symbol lookup error: /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5: undefined symbol: _ZN22QWindowSystemInterface24setPlatformFiltersEventsEb, version Qt_5_PRIVATE_API

grepping for the missing symbol on the output of nm -D shows that it exists in libQt5Gui.so

Same host, with a purely conda install works:

conda create -y --name napari python=3.8 ipython
conda activate napari
conda install -c conda-forge napari

ipython --gui=qt
Python 3.8.5 (default, Sep  4 2020, 07:30:14) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.20.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: 

Differences in packages:

working version

conda list | grep -i qt
pyqt                      5.9.2            py38h05f1152_4  
qt                        5.9.7                h5867ecd_1  
qtconsole                 5.0.2              pyhd8ed1ab_0    conda-forge
qtpy                      1.9.0                      py_0    conda-forge
sphinxcontrib-qthelp      1.0.3                      py_0    conda-forge

problem version

pip list | grep -i qt
PyQt5                         5.15.3
PyQt5-Qt                      5.15.2
PyQt5-sip                     12.8.1
qtconsole                     5.0.2
QtPy                          1.9.0
sphinxcontrib-qthelp          1.0.3

so different qt packages.