In .circleci/config.yml the docker orb is set to version 1.2.1, this version may cause docker image building to fail. Updating the orb to the latest version, currently 2.1.1, has fixed this issue in other projects.

For reference:

• https://circleci.com/docs/2.0/images/linux-vm/14.04-to-20.04-migration/
• https://circleci.com/blog/ubuntu-14-16-image-deprecation/
• [semver:major] Updated default image to ubuntu-2004:202107-02 CircleCI-Public/docker-orb#86