In my case the problem was due to upgrading python version from 3.6 to 3.8.
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.8 2
sudo update-alternatives --config python3
Solved by:
Settings back the python version to 3.6