Any ideas how to fix it?
Error starting daemon: Error initializing network controller: could not delete the default bridge network: network bridge has active end
I had a similar issue after upgrading.
Run
sudo mv /var/lib/docker/network/files/ /tmp/dn-bak
to reset your networks. Then restart docker (sudo systemctl restart docker or sudo service docker restart depending on your OS).
sudo systemctl restart docker
sudo service docker restart
If everything works again you can delete the dn-bak directory.
dn-bak