Problem found. the package 'six' was installed both by pip3 and by apt. The pip3 version in /usr/local/lib/python3.8/dist-packages/six.py was at version 1.11.0, whereas the Ubuntu version is at 1.14.0
Removing the old version fixed the problem. ** Changed in: python-certbot (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1907420 Title: certbot renew fails To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/python-certbot/+bug/1907420/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs