If you run plugins that provide a graphical interface, they will generally pull in wxPython. There's not much we can do to prevent this, I think without disable all python scripting.
Since Ubuntu 18.04 does not provide a GTK2 wxPython, it loads GTK3 wx libraries and crashes KiCad. I would guess that the difference now is that you have updated your system from a previous Ubuntu version.
If you run plugins that provide a graphical interface, they will generally pull in wxPython. There's not much we can do to prevent this, I think without disable all python scripting.
Since Ubuntu 18.04 does not provide a GTK2 wxPython, it loads GTK3 wx libraries and crashes KiCad. I would guess that the difference now is that you have updated your system from a previous Ubuntu version.