I was able to fix it by explicitly setting my context path in nexus.properties. The issue was the connector was creating the wrong internal URL and could not find the repository.
nexus-context-path=/
If you’re having issues with docker login, docker does not function with a non-root path. So you need to make sure you use the HTTP(S) connectors or the Nexus Pro subdomain feature for the docker repositories, and configure your system to use those.