One of the things I've seen is that "The minimum python version was increased to 3.6" in Electrum 3.3.0.
Maybe I'm completely wrong, since I'm far from best with Linux, but this is what I'd start with when checking.
I don't know if "sudo apt-get install python3-setuptools python3-pyqt5 python3-pip" does actually re-install the dependencies, but this can also be an idea.