Segmentation fault on importing from PyQt5 in Py3.10

[ullix]

Using Py3.10 in a venv all worked fine until a few hours ago when I 
ugraded some modules using pip. I believe it was the PyQt* upgrades, 
which created the problem.

Simply opening Py3.10 and importing: PyQt5 ok, but PyQt5.QtWidgets 
results in Seg Fault:
     $ python3
     Python 3.10.0a6 (default, Mar  2 2021, 02:01:08) [GCC 5.4.0 
20160609] on linux
     >>> import PyQt5
     >>> import PyQt5.QtWidgets
     Segmentation fault

Listing with pip gives (only PyQt* items):
     $ pip list
     Package         Version
     --------------- ------------
     ...
     PyQt5              5.15.6
     PyQt5-Qt5       5.15.2
     PyQt5-sip       12.10.1
     ...

Uninstalling every PyQt* item from Py3.10 with pip and reinstalling with 
a requirement.txt file fixing all versions still resulted in the same 
segmentation faults.

requirement.txt:
     ...
     pyqt5       ==  5.15.6
     pyqt5-sip   ==  12.9.0
     ...

Using Py3.9.4 still runs fine, with or without upgrading.Pip list gives:
     PyQt5                  5.15.6
     PyQt5-Qt5           5.15.2
     PyQt5-sip            12.10.1
     PyQtChart           5.15.4
     PyQtChart-Qt5    5.15.2

ullix