If you use CircleCI CLI to build locally and want to troubleshoot, then the --debug option could be of big help.
Please check the below example to know how to use the debug option:
Examples:
circleci --debug config validate
circleci --debug diagnostic
For more help, see the documentation here: https://circleci.com/docs/2.0/local-cli/
If you have any more questions, please submit a ticket to Support or write to support@circleci.com.