Hello Pere,
This issue has also been reported in the FreeCAD forums, and there are
two likely culprits.
One user reported that temporarily moving the ~/.FreeCAD directory and
then launching FreeCAD resulted in the issue no longer occurring, which
would narrow the cause down to some file in that directory.
The other possible issue is the presence of 3rd party extensions,
whether installed from the FreeCAD Community Extras PPA or otherwise,
causing upgrade issues which may or may not have been noticed.
Could you try the "moving ~/.FreeCAD" workaround, and if that doesn't
work, could you provide the output of `ls -l /usr/lib/freecad`?
